The data backup and archive needs on a
personal computer can be overwhelming. People with large hard
drives, numerous application programs installed, and those who
generate a large amount of data should find it necessary to
back up their computers on a weekly or even a daily
basis.
In addition, a critical need on today's
PCs is data storage space. Sometimes it seems the storage
requirements of a PC can never be satisfied. On nearly any PC
used for business, study, or even for fun, the amount of
software installed can quickly overwhelm even a "jumbo" hard
drive. Data used infrequently should be archived to another
storage device to save space on the primary storage
devices.
This chapter focuses on tape backup
drives and removable media disk drives, which increasingly are
used to solve the problems of the growing need for data
storage space and the need for a fast and efficient way to
back up many megabytes of data.
Tape Backup
Drives
Any computer book worth reading warns
repeatedly that you should back up your system regularly.
Backups are necessary because at any time a major problem, or
even some minor ones, can corrupt the important information
and the programs stored on your computer's hard drive,
rendering this information useless. A wide range of problems
can damage the data on your hard drive. Here is a list of some
of these data-damaging problems:
- Sudden fluctuations in the
electricity that powers your computer (power spikes)
resulting in data damage or corruption.
- Overwriting a file by
mistake.
- Mistakenly formatting your hard disk
when you meant to format a floppy.
- Hard drive failure resulting in loss
of data that has not been backed up. Not only do you have to
install a new drive but, because you have no backup, you
also must reinstall your software programs,
disk-by-disk.
- Catastrophic damage to your computer
(storm, flood, lightning strike, fire, theft). A single
lightning strike near your office or home can destroy the
circuitry of your computer, including your hard drive. Theft
of your computer, of course, is equally devastating. A
recent, complete backup greatly simplifies the process of
setting up a replacement computer.
- Loss of valuable data due to a
computer-related virus. One single download could contain a
virus that can damage valuable files and even your entire
hard drive. With several hundred new viruses appearing each
month, no anti-virus software program can keep you entirely
safe. A recent backup of non-infected, critical files can
help repair even the worst damage.
Backups are also the cure for such
common headaches as a full hard drive and the need to transfer
data between computers. By backing up data you rarely use,
then deleting the original data from your hard drive, you free
up the space once occupied by that data. If you later need a
particular data file, you can retrieve that file from your
backup. Sharing large amounts of data between computers--as
when you send data from one city to another, for example--is
more easily accomplished by backing up the data to a tape and
sending the tape.
Regardless of how important regular
backups are, many people avoid making them. A major reason for
this lapse is that for many people, backing up their system is
tedious work when they have to use their floppy disk drive.
When you use your floppy drive, you may have to insert and
remove hundreds of disks to back up all of the important
programs and data, depending on whether your backup software
includes data compression, the capability to specially
encode backed-up data in less space than it takes to store the
same data on your hard drive.
Tape backup drives are the most
simple and efficient device for backing up your system. With a
tape backup drive installed in your system, you simply insert
a tape into the drive, start your backup software, and select
the drive and files you want to back up. The backup software
copies your selected files onto the tape while you attend to
other business. Later, when you need to retrieve some or all
of the files on the backup tape, you insert the tape in the
drive, start your backup program, and select the files you
want to restore. The tape backup drive takes care of the rest
of the job.
This section examines the various types
of tape backup drives on the market, describing the capacities
of different drives as well as the system requirements for
installation and use of a tape drive. The following topics are
covered in this chapter:
- Common standards for tape backup
drives, including QIC-40 and QIC-80 drives
- Common backup tape
capacities
- Newer higher-capacity tape
drives
- Common tape drive
interfaces
- The QIC standards for tape backup
drives
- Portable tape drives
- Tape backup software
The Origins of
Tape Backup Standards
The evolution of tape backup standards
is similar to that of standards for many computer components.
Using tape to back up computer data became a common practice
long before accepted tape backup standards existed. At first,
reel-to-reel systems (somewhat similar to old reel-to-reel
audio tape recorders) were used to store data. The most
commonly used tape--quarter-inch--eventually developed
into a de facto standard. But each tape system manufacturer
used its own data-encoding specifications for backup tapes.
Variations included not only the number of tracks and data
density on the tape, but also the interface used to connect
the drive to the computer.
In 1972, more than a decade before the
introduction of the first IBM-PC, the 3M company introduced
the first quarter-inch tape cartridge designed for data
storage. The cartridge measured 6x4x5/8 inches. Inside this
cartridge, the tape was threaded onto two reels. The tape was
moved from one reel to another during the recording or
read-back process by a drive belt. Because of the reliability
of this tape cartridge, the demand for tape backup systems
began to grow, despite the lack of established standards for
storing data on these cartridges.
The result of this lack of
standardization was that quarter-inch tapes written on one
manufacturer's tape backup drive generally could not be read
on another manufacturer's quarter-inch tape drive. One problem
created by this situation was that the way particular
manufacturers encoded data on a tape continued to change. If a
particular model of tape drive became disabled and the
manufacturer had discontinued that particular drive and no
longer used its encoding format, the data stored on tapes
written on the disabled drive could be unavailable until the
drive had been sent for repairs. In the event the manufacturer
could not repair the drive, the data was lost
forever.
As with other computer components, such
as hard drive interface cards, consumers were the force behind
standardization. Consumers clamored for standardized tape
drives that could read tapes created on different tape drives
manufactured by different companies.
The QIC
Standards
In response to this demand for
standardization, the tape drive industry formed the
Quarter-Inch Cartridge Drive Standards Inc., sometimes simply
referred to as the Quarter-Inch Committee (QIC). In
1983-84, the first tape drive based on a QIC standard was
shipped: the QIC-02, which stored 60M of data encoded
in nine data tracks on roughly 300 feet of tape.
As the technology improved, and because
the 4x6x5/8-inch size of the first tape cartridges was
difficult to adapt to the 5 1/2-inch drive bays in most
IBM-compatible PCs, QIC adopted a second standard for tape
cartridges roughly the size of an audio cassette. These
mini-cartridges measure roughly 3 1/4x2 1/2x3/5
inches.
These two cartridge sizes are currently
used in various QIC-standard tape drives. A two-letter code at
the end of the QIC standard number designates whether the tape
standard is based on the full-sized cartridge or the
mini-cartridge. These two-letter codes are shown in the
following:
- DC in a QIC standard number
stands for data cartridge, the 4x6x5/8-inch
cassette.
- MC in a QIC standard number
stands for mini-cartridge, the 3 1/4x2 1/2x3/5-inch
cassette.
The new QIC-5B-DC, for example, is a
5G-capacity tape based on the QIC standard for the full-sized
cartridge. The new QIC-5010-MC, which has 13G capacity, is
based on the mini-cartridge standard.
Table 18.1 shows the common
QIC-standard tape formats and their technical
specifications.
Unlike software whose version numbers
(1.0, 1.1, 2.0, 2.1) tell you which version of the software is
the most recent, the QIC number designation does not serve as
an accurate guide to understanding which QIC-standard tape
drives are the latest technology. The designations QIC-100 and
QIC-128, for example, were used for tape drives marketed long
before today's QIC-40 and QIC-80 drives. Furthermore, the
QIC-standard version numbers frequently have no correlation
with the capacity of the tape cassettes or mini-cartridges
used with a drive bearing a QIC designation. For example, the
QIC-40 tapes have a capacity of 60M; the QIC-80 tapes, a
capacity of 120M.
QIC-standard backup tapes are magnetic
media, primarily ferric oxide, and are recorded in a manner
similar to the way data is encoded on your hard drive, using
either modified frequency modulation (MFM) or run-length
limited (RLL) technologies.
Table 18.1 Specifications
of QIC-standard Quarter-inch Tape Cassettes and Minicartridges
QIC Minicartridge Tape Standards DC-2000 QIC Tape Standards
(Approximate Dimensions 3 1/4-by-2 1/2-by-3/5)
QIC Standard Number |
Capacity (w/o Compression) (1) |
Tracks |
Data Transfer Rate
(Approximate) |
Data Density |
Tape Length (2) |
Encoding Method |
Interface Type |
QIC-40 |
40MB/60MB |
20 |
2MB-to-8MB |
10,000bpi |
205 ft. |
MFM |
Floppy or optional |
|
|
|
minute |
|
/307.5 ft. |
adapter card |
|
QIC-80 |
80MB/120MB |
28 |
3MB-to-9MB |
14,700bpi |
205 ft./ |
MFM |
Floppy or optional |
|
|
|
minute |
|
307.5 ft. |
|
adapter card |
QIC-100 |
20MB/40MB |
12 or 24 |
-- |
10,000bpi |
-- |
MFM |
SCSI (4) or QIC |
(obsolete) |
|
|
|
|
|
|
|
QIC-128 |
86MB/128MB |
32 |
-- |
16,000bpi |
-- |
MFM |
SCSI or QIC |
QIC-3010 |
255MB |
40 |
9MB minute |
22,000bpi |
300 ft. |
MFM |
Floppy or IDE |
QIC-3020 |
500MB |
40 |
9MB minute |
42,000bpi |
400 ft. |
MFM |
Floppy or IDE |
QIC-3030 |
555MB |
40 |
|
51,000bpi |
275 ft. |
MFM |
SCSI-2 or QIC |
QIC-3040 |
840MB (3) |
42 or 52 |
|
41,000bpi |
400 ft. |
RLL |
SCSI-2 or QIC |
QIC-3050 |
750MB |
40 |
|
-- |
295 ft. |
RLL |
SCSI-2 or QIC |
QIC-3060 |
875MB |
38 |
|
-- |
295 ft. |
RLL |
-- |
(inactive) |
|
|
|
|
|
|
|
QIC-3070 |
4GB |
144 |
|
68,000 |
295 ft. |
RLL |
SCSI-2 or QIC |
QIC-3080 |
1.6GB |
50 |
|
60,000 |
-- |
RLL |
SCSI-2 or QIC |
QIC-3110 |
2GB |
48 |
|
-- |
-- |
RLL |
SCSI-2 or QIC |
QIC-5010 |
13GB |
144 |
|
-- |
-- |
RLL |
SCSI-2 or QIC |
QIC-11 |
45MB |
9 |
-- |
-- |
450 ft. |
MFM |
QIC-02 |
(DC-300) |
|
|
|
|
|
|
|
QIC-24 |
45MB/60MB |
9 |
-- |
8,000 |
450 ft. |
MFM |
SCSI or QIC-02 |
|
|
|
|
|
600 ft. |
|
|
QIC-120 |
125MB |
15 |
-- |
10,000 |
600 ft. |
MFM |
SCSI or QIC-02 |
QIC-150 |
150MB/250MB |
18 |
-- |
10,000bpi |
600 ft. |
MFM |
SCSI or QIC-02 |
|
|
|
|
|
1,000 ft. |
|
|
QIC-525 |
320MB/525MB |
26 |
12MB minute |
16,000bpi |
1,000 ft. |
MFM |
SCSI or SCSI-2 |
QIC-1000 |
1GB |
30 |
18MB minute |
36,000bpi |
760 ft. |
MFM |
SCSI or SCSI-2 |
QIC-1350 |
1.35GB |
30 |
18MB minute |
51,000bpi |
760 ft. |
RLL |
SCSI-2 |
QIC-2100 |
2.1GB |
30 |
18MB minute |
68,000bpi |
875 ft. |
RLL |
SCSI-2 |
QIC-2GB |
2.0GB |
42 |
18MB minute |
40,640bpi |
900 ft. |
MFM |
SCSI-2 |
QIC-5GB |
5GB |
44 |
18MB minute |
96,000bpi |
1,200 ft. |
RLL |
SCSI-2 |
QIC-5010 |
13GB |
144 |
18MB minute |
68,000bpi |
-- |
RLL |
SCSI-2 | (1) Tape capacity may vary according to tape
length. (2) Tape lengths may vary by manufacturer.
*Tape capacity may vary according to tape
length. **Tape lengths may vary by manufacturer. ***1GB
with drives based on 0.315-inch tape cartridge. ****SCSI:
Small Computer Systems Interface.
Common QIC Tape
Backup Types
The most common QIC-standard drives,
QIC-40 and QIC-80, are based on mini- cartridges. Millions of
drives based on the QIC-40 and QIC-80 standards are currently
installed in computer systems. There are several reasons for
the success of QIC-40 and QIC-80, not the least of which is
that these two standards resulted in the first generation of
economically attractive tape drives which stored data in a
manner compatible from one manufacturer to another. In other
words, QIC-40 and QIC-80 tape drives and tapes are quite
affordable, and backups made on one QIC-40 or QIC-80 tape
drive can b0e read in a tape drive built by another
manufacturer.
In addition, the compact size of the
mini-cartridge used for QIC-40 and QIC-80 tapes has resulted
in drives made by numerous manufacturers that fit easily into
both 5 1/2-inch half-height drive bays and 3 1/2x1-inch drive
bays. Portable tape drives that read and write QIC-80 format
tapes are quite common, but QIC-40 drives are near extinction.
Unlike a drive that is installed in a computer's drive bay,
portable drives can be used to back up any number of
computers.
Another reason for the success of
QIC-40 and QIC-80 tape drives is that the cost of tapes
themselves is considerably lower per megabyte than the cost of
a stack of floppy disks that can store the same amount of
backup data. For example, a name brand QIC-80 tape that can
hold 250M of data (with data compression) costs between $14
and $25. The street price of 13 boxes (10 per box) name brand
1.44M 3 1/2-inch floppy disks, which hold roughly the same
amount of compressed data, is about $90. The same number of
generic, bulk floppy disks, which many people are hesitant to
rely upon for backing up important data, costs nearly $50. Of
course, the price difference doesn't include the valuable time
spent swapping those disks or the relative cost of storing
them.
Most of the QIC-80 drives on the market
today have one major shortcoming--the use of the floppy drive
interface, especially on an older PC, makes the tape drive
performance extremely slow. Data transfers occur at roughly
the same slow rate as when data is written to a floppy disk.
Controllers that support only the Double Density (DD) floppy
drives can only write data at 250Kbps, which is fewer than 2M
(millions of bytes) per minute. A floppy controller that
supports HD (High Density) drives can operate at 300 or
500Kbps, which is up to 3.75M per minute. The latest ED
(Extra-high Density) controllers can operate at rates of up to
7.5M per minute, which is quite good (see Table 18.2). Note
that these rates are the maximum raw throughput of the
controller, and due to overhead you will never achieve these
actual figures in practice.
Table 18.2 Floppy
Controller Raw Data Transfer Rates
Controller Type |
DD |
HD |
HD |
ED |
Transfer rate in kilobits per second
(Kbps) |
250.00 |
300.00 |
500.00 |
1,000.00 |
Transfer rate in kilobytes per second
(K/sec) |
31.25 |
37.50 |
62.50 |
125.00 |
Transfer rate in megabytes per second
(M/sec) |
1.88 |
2.25 |
3.75 |
7.50 |
Backup tapes, like floppy disks and
hard drives, must be formatted before use. And one aspect of
using a QIC-80 tape drive that has not been improved is the
time it takes to format a tape. Formatting a 125M length
QIC-80 tape can take more than three hours. It's almost
impossible to find an unformatted tape because of these long
format times. The industry has been preformatting tapes since
1994. Other tape formats have the ability to format
on-the-fly, which means they don't require preformatted
tapes.
Data is stored on QIC-40 and QIC-80
tapes in MFM format, the format used on floppy disks (and
older hard drives). Another similarity between formatting a
backup tape, floppy disks, or a hard drive is that the
formatting process creates a record-keeping system. The
record-keeping system used on QIC-40 and QIC-80 tapes is
similar to that on a hard drive or floppy disk.
The QIC standard calls for a file
allocation table (FAT) that keeps track of where data is
stored on the tape and keeps bad sectors from being used for
data storage. A QIC-40 tape is divided into 20 tracks, with
each track divided into 68 segments of 29 sectors each. Each
sector stores 1K (1,024 bytes). This record-keeping system and
the error-correcting system that ensures reliably stored
backup data use a total of 30 percent or more of each QIC-40
tape.
Despite the slow backup speeds of tape
backup drives on some computers and the time it takes to
format tapes, the ease of using a backup tape drive makes it
easy to understand the popularity of QIC-40 and QIC-80 tape
drives. And that popularity has its benefits. Prices of QIC-80
tape drives--the smallest-capacity tape drives anyone should
consider--have plunged in recent years. Brand-name QIC-80 tape
backup drives often cost less than $150; sometimes you can buy
them for as little as $100 by shopping mail order.
QIC-40 Drives
The first tape backup drives to gain
wide acceptance were based on the QIC-40 standard, adopted in
1986. Most early QIC-40 tape drives were built to fit a 5
1/2-inch drive bay. The QIC-40-standard drives use an internal
power connector and send and receive data through a cable
linked to the floppy controller generally. The first QIC-40
tapes, which had a native capacity of 40M (they could
hold 40M of data without data compression), were soon followed
by QIC-40 tapes capable of holding 60M without data
compression.
One disadvantage of the first QIC-40
tape drives was that because a spare connector had to be used
on the floppy drive cable, only one floppy drive could be used
on a system in which a tape drive was installed. But with the
use of a special cable, more recent QIC-40 drives are
installed easily on systems with two floppy drives.
Although a major goal of the QIC
organization was to achieve compatibility between tape backup
systems, a tape created on one brand of tape drive could not
necessarily be read in another brand. Manufacturers still
clung to their individual arrangements for the physical
placement of data on the tape. The goal of compatibility
between tape backup systems became more of a reality with the
introduction of QIC-80 drives.
QIC-80 Drives
The QIC-80 tape backup drive is the
most popular tape backup drive on the market and the minimum
any buyer should consider. QIC-80 tape drives generally are
built to fit 3 1/2x1-inch bays, although they usually include
a frame and faceplate that enable them to be used in a larger
5 1/2-inch bay. Like the QIC-40 drives, QIC-80 tape systems
use an internal power connector. The data connection for a
QIC-80 tape backup can be the same type of floppy disk
controller connection used for QIC-40 drives, or a special
high-speed interface installed in an available expansion slot
on the motherboard. The use of a high-speed interface card
greatly can increase the data transfer rate and decrease the
amount of time needed for a backup.
Generally, a tape created on one brand
of QIC-80 tape drive can be read and written to by another
manufacturer's drive. This improved compatibility is due in
large measure to the QIC-80 standard itself, which specifies
not only the type of record-keeping system for each tape, but
also the logical data structure of the tape. QIC-80-standard
drives can read, but not write, QIC-40 tapes.
Portable Tape Drives
The portable tape drive is one
of the most popular tape drive configurations because
portables can be moved easily from system to system--desktops,
laptops, a single system, or multisystem installations.
Portable tape drives are particularly useful to people who use
laptops (in which an internal tape backup drive will not fit)
and those who want to back up a number of systems on a single
tape backup drive. Portable tape drives are good also for
people who want to use a tape backup drive for their desktop
system but whose system has no available drive bay, as is
often the case with small profile, or slimline, desktop
systems.
Portable tape drives can meet so many
needs because these drives are self-contained. The drive
itself is contained in a rectangular box. The unit connects to
the computer's parallel port and is powered by a transformer
that plugs into a common AC socket.
To set up a portable tape drive, you
simply plug the transformer cord into the system unit and an
AC socket, connect the data cable to the computer's parallel
port, and run the backup software. One limitation of portable
units is availability of compatible backup software. Although
portable tape drive manufacturers include software that
operates the drive, some popular third-party backup software
cannot be used with portable drives.
The most popular portable tape drives
are available in QIC-80 standards. These models can achieve a
data transfer rate of 3M to 6M per minute.
Newer
High-Capacity QIC-Standard Drives
Using a QIC-80 tape drive to back up a
network server's 4G drive or other large hard drive packed
with data can be as frustrating as swapping floppies during a
backup on a system with a more common 200M-500M drive. To back
up a 4G network server hard drive with a QIC-40 tape drive
without using data compression, for example, you need about 64
tapes. With data compression, the number of tapes drops to
32--but making the backup takes longer.
The solution to this tape-swapping
problem is to use a larger-capacity tape drive system. QIC has
established a number of standards for higher-capacity tape
drive systems ranging from 86M to 13G. Generally, these
larger-capacity systems pack data more densely on the tape,
using as many as 144 tracks to pack 60,000 bits per inch (bpi)
or more onto the tape (compared to the QIC-40's 20 tracks and
10,000 bpi). To achieve these higher capacities, QIC-standards
call for tape media with a higher coercivity level of 1,300
oersted or more (compared to QIC-40 and QIC-80 tape media,
which has a coercivity level of 550 oersted). High-capacity
tapes are also longer. QIC-5010 tapes, for example, are 1,200
feet long (compared to QIC-40 and QIC-80 tapes, both of which
are roughly 300 feet long).
NOTE: Just as the higher
coercivity level of 1.44M floppy disks enables an HD drive
to write more densely packed tracks than is possible with
720K floppy disks, higher-coercivity tape media enables
higher densities as well.
Although tape systems based on the
mini-cartridge dominate the market for lower- capacity tape
drives (the QIC-40 60M and QIC-80 120M systems), high-capacity
tape backup systems are based on both mini-cartridge-sized
tapes and full-sized data cartridge tapes. For example, the
QIC-525 standard, which has a capacity of 525M (without data
compression), is based on the full-sized (4x6x5/8) cartridge.
The QIC-5010 standard is based on a mini-cartridge (3 1/4x2
1/2x3/5).
QIC-Tape
Compatibility
Although QIC-standard drives are based
on the standard mini-cartridge and the full-sized data
cartridge, it would be a mistake to assume that tapes based on
the same cartridge standard are always compatible. For
example, QIC-5010-standard tapes are incompatible with QIC-40
and QIC-80 tape backup systems, although both standards are
based on the mini-cartridge. Similarly, QIC-525-standard tapes
are incompatible with earlier standards based on the
full-sized data cartridge. The lack of compatibility between
tapes based on the same sized cartridge is due to differences
in tape drive mechanisms, as well as the coercivity
differences between tape standards. Table 18.3 shows the
compatibility of common QIC-standard backup tapes.
Tape compatibility is an important
issue to consider when you choose a tape backup system. For
example, as you can see from Table 18.3, the 4G
QIC-3070-standard drive can read only its own tapes and those
that conform to the QIC-3030 standard. If you have many QIC-80
tapes containing data that you must be able to continue to
access, a better choice might be a drive based on the 2G
QIC-3010 standard. The QIC-3010 can read QIC-40 and QIC-80
tapes. This chapter's "Choosing a Tape Backup Type" section
covers similar issues to be considered when you purchase a new
tape backup drive.
Table
18.3 QIC-Tape-Standard Compatibility
QIC Mini-Cartridge Standard |
Compatibility |
QIC-40 |
N/A |
QIC-80 |
QIC-40 (read-only) |
QIC-100 |
N/A |
QIC-128 |
QIC-100 (read-only) |
QIC-3010 |
QIC-40 and QIC-80 (read only) |
QIC-3030 |
QIC-3010 (read-only) |
QIC-3070 |
QIC-3030 (read-only) |
QIC-24 |
N/A |
QIC-120 |
QIC-24 (read-only) |
QIC-150 |
QIC-24 and QIC-120 (read-only) |
QIC-525 |
QIC-24, QIC-120, and QIC-150
(read-only) |
QIC-1000 |
QIC-120, QIC-150, and QIC-525
(read-only) |
QIC-1350 |
QIC-525 and QIC-1000 (read-only) |
QIC-2G |
QIC-120, QIC-150, QIC-525, and QIC-1000
(read-only) |
QIC-2100 |
QIC-525 and QIC-1000 (read-only) |
QIC-5G |
QIC-24, QIC-120, QIC-150, QIC-525, and
QIC-1000 (read-only) |
QIC-5010 |
QIC-150, QIC-525, and QIC-1000
(read-only) |
Other
High-Capacity Tape Drive Standards
Although ferric oxide QIC-standard
tapes continue to be popular, two other types of tape backup
systems are becoming increasingly popular for backing up
networks and other systems with large amounts of data: 4mm
digital audio tape (DAT) and 8mm videotape.
Sony, which introduced DAT tape,
licenses DAT tape technologies to other manufacturers, in
effect setting the standard for drives and tapes manufactured
by those companies. There is only one company, Exabyte, which
manufacturers 8mm tape drive assemblies. As a result, you're
assured compatibility. Table 18.4 shows the basic
specifications of the DAT and 8mm technology tapes.
Helical scan recording is
similar in many ways to the way video images are recorded to
videotape. As with QIC-standard tape drives, DAT and 8mm tapes
move past the recording heads, which are mounted on a drum.
These read/write heads rotate at a slight angle to the tape,
writing a section of a helix, or spiral. The tape drive
mechanism wraps the tape about halfway around the read/write
heads, causing the heads to touch the tape at an angle. With
helical scan technology, the entire surface of the tape is
used to record data, unlike other technologies in which data
tracks are separated by areas of unrecorded tape. This use of
the entire tape surface enables helical scan backup drives to
pack a much greater amount of data on a particular length of
tape.
Table 18.4 DAT and 8mm Tape
Specifications
Tape Standard |
Capacity (w/o Compression) |
Data Density |
Tracks (Approximate) |
Tape Length |
Recording Technology |
Encoding Format |
Interface |
DAT tape (4mm metal particle) |
2G/4G |
114Mbit |
1,869 |
195 ft./300 ft. |
Helical Scan DataDAT |
DDS* |
SCSI |
8mm video tape |
14G |
NA |
NA |
120m |
Helical Scan |
|
| *DDS:
Digital data storage
The DAT Tape Drive Standard
DAT (Digital Audio Tape) is a
tape standard that has primarily been developed and marketed
by Hewlett-Packard. HP chairs the DDS (Digital Data Storage)
Manufacturers Group and has led the development of the DDS
standards.
The technology behind digital audio
tape is similar in many ways to the techniques used to record
music and encode it on musical compact discs (CDs). Data is
not recorded on the tape in the MFM or RLL formats used by
QIC-standard drives; rather, bits of data received by the tape
drive are assigned numerical values, or digits. Then these
digits are translated into a stream of electronic pulses that
are placed in the tape. Later, when information is being
restored to a computer system from the tape, the DAT tape
drive translates these digits back into binary bits that can
be stored on the computer.
DAT tapes can store up to 12G of
uncompressed data, or about 24G compressed. Two types of data
formats--DDS and DataDAT--are used for DAT tapes; however, DDS
type drives are by far the most common. DDS drives are
available in three types:
- DDS-1 drives store 2G of
uncompressed data (4G compressed).
- DDS-2 drives can store 4G of
data uncompressed (up to 8G with
compression).
- DDS-3 drives have a native
12M capacity, or 24M compressed.
The new DDS-3 drives offer full read
and write compatibility with all DDS-2 and DDS-1 drives. DDS-3
offers three times the capacity and double the data-transfer
rates of current DDS-2 drives. DDS-3 drives are designed to
provide reliable high-performance backup for medium to large
networks at a substantially lower price than 8mm or DLT
(digital linear tape) products with similar
capacities.
The new HP DDS-3 drive (Model C1537A)
has a native capacity of 12G with a transfer rate of 1M/sec.
The DDS-3 drive typically can store 24G on a single 125m tape
at a rate of 2M/sec using built-in hardware data compression.
The new HP DDS-3 drive incorporates several innovations,
including the use of a Partial Response Maximum
Likelihood (PRML) data-channel detection scheme
that enables the tape's read head to differentiate between
bits of data picked up simultaneously.
A typical DDS-2 drive costs about $750,
while DDS-3 drives are right around $1,000. DDS technology has
an excellent track record and a reputation for reliability
that has made it the technology of choice for workstation, end
user, and network backup.
The 8mm Tape Drive
A single manufacturer, Exabyte, offers
tape backup drives that take advantage of 8mm videotape
cartridges. These drives are offered in several
capacities--1.5G (3G with hardware data compression), 5G (10G
with hardware compression), 7G (14G with hardware
compression), and 20G (40G with hardware compression)
Although these drives use 8mm
videotapes, video technology is not used in the process of
recording computer data to these drives. Rather, Exabyte
developed its own technology for encoding data on the tapes.
The helical scan method is used to record data to the
tape.
The 6M/sec data throughput rate of the
Exabyte 8mm tape backup drive, compared with the 10M per
minute throughput of the DAT drive, makes the 8mm tape drive a
more attractive choice. The extraordinary speed and huge
capacity of these 8mm tape drives makes them extremely
attractive for backing up network servers and for backing up
workstations from the server.
DLT (Digital Linear Tape)
Over the last year, a new tape
technology has taken off because of its capability to provide
high-capacity, high-speed, and highly reliable backup.
Digital Linear Tape (DLT) is now considered one of the
hottest products in the high-end tape-backup market. DLT
started as a proprietary technology belonging to Digital
Equipment Corporation. The technology has been on the market
since 1991, but in December 1994, Quantum purchased Digital's
DLT and magneto-resistive drive technology.
DLT has a capacity of up to 35-70G
compressed, and a data-transfer rate of 5-10M/sec or more.
This is approximately the same speed as a high speed 8mm
drive; however, 8mm has a slight performance advantage in
real-world tests.
DLT segments the tape into parallel
horizontal tracks and records data by streaming the tape
across a single stationary head at 100-150 inches/sec during
read/write operations. This is a dramatic contrast to
traditional helical-scan technology, in which the data is
recorded in diagonal stripes with a rotating drum head while a
much slower tape motor draws the media past the recording
head.
The result is a very durable drive and
a robust medium. DLT drive heads have a minimum life
expectancy of 15,000 hours under worst-case temperature and
humidity conditions, and the tapes have a life expectancy of
500,000 passes. DLT drives are designed primarily for network
server backup, and cost $6,000 to $8,000 or more depending on
capacity. With automatic tape changers, DLT drives can be left
unattended for many network backup tasks.
Travan Cartridge Tape
3M has created an entirely new tape
cartridge standard based on the QIC format called
Travan. Tape drives based on Travan technology have had
a significant impact on the tape market for PCs and
workstations, and drives based on this technology should
dominate this market over the next several years.
The Travan platform features a unique
drive/mini-cartridge interface that is patented by 3M. The
Travan platform fits in a 3 1/2-inch form factor, making it
easy to install in a variety of systems and enclosures. Travan
drives can accept current QIC and Travan mini-cartridges--a
critical need for users, given the installed base of more than
200 million QIC-compatible mini-cartridges
worldwide.
Travan cartridges contain 750 feet of
.315-inch wide tape. There are currently several different
levels of Travan cartridges and drives available called TR-1
through TR-4, each based on a particular QIC standard:
- The TR-1 mini-cartridge provides
users with 400M of uncompressed storage, more than doubling
the capacity of the industry's top-selling QIC-80
mini-cartridge (125M).
- The TR-2 mini-cartridge, a new
modified QIC-3010 drive/cartridge, stores 800M of
uncompressed data, which is significantly more than the 340M
available in QIC-3010 form.
- The capacity of the TR-3
mini-cartridge, a new modified 3020 drive/cartridge, is 1.6G
of uncompressed data (up from 670M in QIC-3020
form).
- The newest Travan cartridge, TR-4,
stores 4G of uncompressed data! The Travan migration path
for the new drive and mini-cartridge products should exceed
15G of uncompressed storage capacity by 1997, according to
3M.
Notice that virtually all Travan drives
offer 2:1 data compression, which doubles the uncompressed
native capacity. This means that a Travan TR-4 drive can store
up to 8G on a single cartridge! A typical TR-4 based drive,
such as those from Hewlett-Packard's Colorado Memory Systems
Division, sell for under $400. Because Travan tapes sell in
the $40 price range and are available through any of 3M's
worldwide network of distributors and resellers, the low cost
and high availability of these drives and cartridges make
Travan one of the best backup solutions possible for most
individuals.
The TR-1 through TR-3 drives usually
interface to the system via the floppy controller or parallel
port. I recommend using an EPP or ECP parallel port for ease
of use and performance. The higher end TR-4 drives often use a
SCSI-2 interface, which offers greater performance than either
floppy or parallel port interfaces. A typical TR-4 system such
as the HP T4000 drive operates at 514K/sec, which is
approximately four times faster than floppy-interface systems,
providing backup speeds up to 31M per minute native and up to
62M per minute with 2:1 data compression. Using a typical
Pentium system, users can back up a 1G hard drive in about 30
minutes. If you are using the floppy controller or parallel
port, you can expect backup times about four times longer or
about two hours for a 1G drive.
Storage industry leaders such as 3M,
HP/Colorado, Iomega, Conner Peripherals, Exabyte, Tandberg
Data, AIWA, Pertec Memories, TEAC, Rexon, and Sony offer
Travan drives and support future development of Travan drive
and recording formats.
Choosing a Tape
Backup Drive
Choosing a tape backup drive can be a
simple job if you need to back up a single stand-alone system
with a 500M (or smaller) hard drive. The decision becomes more
complex if the system has a larger hard drive, or if you must
back up not only a desktop system but also a laptop. Choosing
a backup tape drive type can be an even more complex program
if you must back up a network server's 4G hard drive and
perhaps even back up the workstations from the server. As you
ponder which backup tape drive type you should choose,
consider the following factors:
- The amount of data you must back
up
- The data throughput you
need
- The tape standard that is best for
your needs
- The cost of the drive and
tapes
- The capabilities and compatibility
of the included driver and backup software
By balancing the considerations of
price, capacity, throughput, compatibility, and tape standard,
you can find a tape drive that best meets your needs.
NOTE: When purchasing a tape
backup drive, take the time to look through magazines where
dealers or distributors advertise. Several publications
specialize in PCs and carry advertising from many hardware
and software distributors. I recommend publications such as
the Computer Reseller News, Computer Hotline, The Processor,
and Computer Shopper. These publications cater to people or
companies willing to go around the middlemen and buy direct.
By reading such publications, you can get an excellent idea
of the drives available and the price you can expect to
pay.
While reading about drive
capabilities and prices, don't neglect to read reviews of
the software included with each drive. Verify that the
software capabilities match your expectations and needs.
This is especially important if you intend to use the drive
on a non-Windows 95 system, because most backup software is
tailored for Windows 95 systems.
Capacity
The first rule for choosing a tape
backup drive is to buy a drive whose capacity is large enough
for your needs, now and for the foreseeable future. The ideal
is to buy a drive with enough capacity that you can start your
backup software, insert a blank tape in the drive, walk away
from the system (or go about other work), and find the backup
completed when you return. You can safely store the tape and
resume working.
Given that ideal, an internal QIC-80
drive might be just the ticket if you need to back up a single
system with a hard drive of 250M or less. If you need to back
up several systems, including laptops, with hard drives of
250M or less, a portable QIC-80 drive might be the
solution.
If you must back up a large network
server hard drive, relying on a QIC-80 tape drive with its
125M capacity (250M with software data compression) is a bad
idea. A better choice would be one of the larger-capacity tape
backup drive systems detailed earlier in "Other High-Capacity
Tape Drive Standards."
Lately, no matter what the capacity
needs for a workstation, I have been recommending either DAT
drives or the newer Travan drives. These are simply the most
cost-effective, highest-performing drives on the market today.
The tapes are preformatted, which saves a lot of time, and can
store up to 8G on a single Travan TR-4 tape or 24G on a single
DDS-3 DAT tape.
You should always make sure that your
tape backup media supports a capacity larger than your largest
single drive or partition. This will make automated backups
possible because you won't have to change a tape in the middle
of a backup. Because the DAT drives normally interface via
SCSI, you can use a parallel port SCSI adapter to connect the
drive to a system's parallel port as well as an internal SCSI
adapter. Of course, the internal adapter will perform better,
but a portable DAT drive connected via the parallel port can
be used to back up many different systems. The DAT media is
also cheaper than any other media.
Tape Standards
The next most important consideration,
after adequate capacity, is choosing a drive whose tapes meet
a standard that is useful to you. For example, if you must be
able to restore backup data using any of a number of different
tape backup drives, you should ensure that all these drives
can at least read the tapes. For this reason, if you have
several systems to work with, you should choose a tape
standard that will work in them all.
There is no quick, simple answer as to
which standard is the best. Many people stick with
QIC-standard drives because QIC created the first standards
and continues to develop new standards for large-capacity tape
backups. But if you need a large-capacity backup tape system,
DAT or 8mm may be the correct choice.
If you need backward compatibility with
tapes or tape drives you already have, you will need to buy
drives that are the same standard or a higher compatible
standard. For example, if you need a large-capacity tape drive
that is backwardly compatible with your QIC-80 tapes, you
should consider the 2G-capacity QIC-3010, which reads QIC-40
and QIC-80 tapes. If, on the other hand, you don't have to
worry about data already stored on old tapes, the important
considerations may be capacity and performance. Therefore, DAT
or 8mm drives may be the best choice.
TIP: It is important that you
make a choice you can live with. If you manage a large
installation of computers, mixing QIC, Travan, DAT, and 8mm
drives among systems is seldom a good idea.
Software Compatibility
Equally important to your consideration
is the software required to operate each drive. Currently,
most drives come with software that runs under the Windows 95
operating system. However, finding software that runs equally
well under Windows NT or UNIX might be difficult.
Most operating systems have their own
software for backing up data to a tape drive. If you intend to
use this software, you should verify that the drive you
purchase is supported by each piece of software on each system
that you intend to use the drive with.
NOTE: For more information on
tape drive software, see "Tape Drive Backup Software" later
in this chapter.
Data Throughput
You should consider the 8mm or DLT
drives if performance is more important to you than price or
compatibility. These drives offer huge capacity and tremendous
data throughput--as high as 6M/sec. Large-capacity drives
based on newer QIC-standards are capable of 18M per minute
throughput. DAT tape drives offer throughput of 10M per
minute.
The low end of the tape backup drive
performance spectrum is older QIC-80 standard drives. When
linked to a floppy controller, these drives achieve 3M to 4M
per minute throughput. Even with a dedicated interface card
purchased at added cost, QIC-80 drives are lucky to achieve
their advertised throughput of 9M per minute. Portable QIC-80
drives are advertised at 3M to 8M per minute, but 2M or 3M a
minute is a more realistic figure.
The Cost of the Drive and
Tapes
The price of tape drives varies
considerably based upon where you buy, so it pays to shop
enthusiastically for price after you have settled on the type
of drive you want to buy.
The cost of backup tapes also varies
widely, depending on where you buy. The same name-brand 12G
DAT tape that costs as much as $14 from one vendor can cost
$12 from another. The cost of a formatted name-brand QIC-80
(120M) tape can range from $15 to $26, depending on where you
buy it. Because many computer retailers and direct channel
vendors offer lower prices when you buy three or more tapes at
a time, it pays to shop for price and buy the largest quantity
of tapes you expect to need.
TIP: One point worth remembering
when you evaluate whether to buy a tape drive is that the
cost of the tapes and drive, taken as a whole, is nowhere
near as high as the costs (in terms of frustration and lost
productivity) of a single data-damaging hard drive problem.
Considering that most people are more likely to back up
their system if they have a tape drive installed than if
they must use floppy disks for the backup, the cost of a
drive and tapes is quite small, even on a stand-alone PC
used mostly for fun.
Tape Drive
Installation Issues
Each of the tape drive standards
covered in this chapter provides a range of options for
installation. These options include both internal and external
installation. Whether to choose an internal or external drive,
and which external drive to choose if that appears to be the
best choice for you, is not always a cut-and-dried issue. If
you must back up a single computer with a relatively small
hard drive (500M or less), an internal QIC-80 drive might be
your best choice. If you have to back up several computers
with 500M hard drives, or if you must be able to share data
between several computers, you might be able to make do with a
QIC-80 portable. If your backup needs are not that simple,
however, here are some additional considerations:
- If your computer has a large hard
drive and you back up often, or if you administer a large
number of systems and want to minimize the amount of work
you must do and the number of tapes you have to store for
each computer, installing large-capacity QIC, DAT, or 8mm
tape drives in each computer might be what you need to
do.
- If your best choice is a large
capacity QIC, DAT, or 8mm tape drive and almost all the
computers you administer have an available drive bay, you
might choose a portable DAT or 8mm tape system, which can be
moved from system-to-system.
CAUTION: Steer away from
nonstandard tape backup drives. For example, some drives may
not conform to QIC, DAT, or Exabyte standards. Because
Exabyte is the only manufacturer of 8mm tape backup drives,
you can be confident that tapes made on this manufacturer's
drives can be read on their drives. I would avoid drives
based on VHS videotape, for example, because these types of
drives are not a true standard and are not very
well-supported.
The following sections cover some
important installation issues for internally- and
externally-mounted drives.
Internal Installation
Virtually all internal tape backup
drives available today are designed to be installed in a
half-height drive bay. Many are designed to be installed in
either half-height drive bays or the smaller drive bays
generally used for 3 1/2-inch floppy drives. Drives that can
be installed in 3 1/2-inch floppy drive bays generally are
shipped in a cage, or frame, that enables them to be
installed in a 5 1/4-inch bay. To install the drive in a 3
1/2-inch bay, you remove the cage and the 5 1/4-inch bay
faceplate. Most tape drives are between about 5 and 9 inches
deep; they require approximately 5-9 inches of clearance
inside the system case. To mount tape drives inside the
system, use the same rails or cage apparatus used for floppy
drives, hard drives, and devices such as CD-ROM drives.
NOTE: Remember that the drive bay
you select needs to have access to the outside of the
machine!
NOTE: Half-height drive bays
measure roughly 1.7 inches high by 5.9 inches wide. The
smaller drive bays measure 1x4 inches.
Internal tape drives require a spare
power connector, usually the larger connector used for hard
drives, although some may require the smaller power connector
common to 3 1/2-inch floppy drives. If a power connector is
not available inside your system, you can buy a power splitter
from a computer store or cable supply vendor. A power
splitter looks like the letter Y and acts like an
extension cord. You unplug the power connector from a device
(such as a floppy drive) that's already installed. Then plug
the bottom point of the Y into that power connector. The two
arms of the Y then provide you with two power connectors.
NOTE: More information about
power connections for drives is available in Chapter 17,
"CD-ROM Drives."
Internal tape drives also require an
interface to the system. QIC-40 and QIC-80 drives most often
connect to the system through the floppy controller. On a
system with only one floppy drive, you connect the tape drive
to an unused connector on the floppy disk data cable. On
systems with two floppy disk drives, you use a special cable
linked to the floppy disk data cable--in effect, a splitter
cable.
Internal drives other than QIC-40s and
QIC-80s usually require a special adapter card, or they may
link to a card already installed in your system. This card is
usually one of the following: a QIC-standard adapter card, a
Small Computer Systems Interface (SCSI) adapter, a SCSI-2
adapter card, or an Integrated Drive Electronics (IDE) card.
When purchasing a drive, you must determine which interface
you need; make sure that the drive kit includes the adapter
card you need or that you purchase the correct card.
External Installation
If you want to move an external tape
drive from computer to computer, you must install an adapter
card in each system on which you want to use the tape drive.
Portable tape backup drives such as the DAT portables have a
SCSI-to-parallel port converter that uses the computer's
parallel port connector. Adapter cards designed for use with
external tape drives have a different connector, depending on
the interface used, that is accessible from the back panel of
the system unit. These cards are generally QIC-standard, SCSI,
SCSI-2, or IDE.
When you buy an external tape backup
drive that requires an adapter, you must ensure either that
the drive includes the necessary adapter card or that you
purchase the card at the same time you purchase the drive. In
addition, if you plan to use the external tape drive to back
up a number of systems, you must buy a card for each system on
which you plan to use the drive.
Power is supplied to external units by
a transformer that plugs into an ordinary 120v AC wall socket.
Generally, the transformer connects to the external tape drive
with a small connector. When you choose an external tape
drive, be sure you have enough AC power sockets available for
your computer, its peripherals, and the tape drive.
Tape Drive
Backup Software
The most important decision you can
make after you choose the tape standard and capacity of your
backup tape drive is the backup software you will use with it.
Most tape drives are shipped with backup software that
generally is adequate for your basic backup needs.
Often, however, third-party software
compatible with the drive you have chosen gives you greater
flexibility and functionality. For example, some tape drives
may be shipped with only DOS-based software. If you want to
use one of these drives from within Windows, or on a system
running OS/2 or UNIX, you may need to purchase third-party
backup software. And if you will be backing up network
workstations from a server, you must make sure that the drive
is shipped with software capable of performing this function;
otherwise, you will need to acquire third-party
software.
One important issue with backup
software is data compression, special programming that
stores data on the backup tape in less space than is needed on
the original source disk that is provided with most backup
software. Some companies produce backup software that is
well-known for especially efficient data compression. In other
words, backup software produced by these companies does a
better job of compressing large data files into a small amount
of space.
NOTE: The backup software built
into Windows 95 supports a variety of QIC 40, 80, and 3010
tape drives that are connected via the floppy controller
card, as well as the Colorado Memory Systems QIC 40, 80, and
3010 drives attached via the parallel port. Unfortunately,
the Windows 95 backup does not support the majority of tape
drives currently on the market! For example, SCSI tape
drives of any kind are not supported, and neither are the
newer QIC-type drives such as 3020 or Travan. Fortunately,
many superior backup programs are available from aftermarket
sources. Most of the time, you will get this software with
the drive itself. Check with your tape drive manufacturer to
verify Windows 95 support.
You may want to take the time to read
reviews on backup software in one of the many monthly computer
magazines, such as PC Magazine, Windows
Magazine, or BYTE Magazine. The reviews can help
you determine which backup software does the best job of
compressing data; they also provide information on how quickly
backup software programs perform a typical backup. The speed
of the backup software and its data-compression capabilities
are important considerations. Also of great importance is
whether the software is easy to use. If your backup software
makes backing up more difficult than it has to be, chances are
you won't back up as often as you should.
TIP: Some of the more recent
software for tape drives include a "Disaster Recovery"
feature. This feature creates a boot disk (floppy) that can
be used to quickly reformat a drive and install a basic
Windows 95 platform for use with the drive. Look for this
feature when considering your purchase decision.
Bundled Software
Before you buy a backup tape drive, you
should always check whether the drive includes software that
will meet your needs and, if it doesn't, be sure to buy
third-party software that does the job. Generally, the
software bundled with most tape backup drives will do the job
for you--provided that you don't plan to place great demands
on the tape drive.
The software included with a QIC-80
drive, for example, generally cannot be used to back up
network workstations from the server. If you want to use a
QIC-80 drive for this task, you may need to buy special
software compatible with your network and the tape backup
drive. If you use Windows, Windows NT, OS/2, or UNIX, your
backup software must be compatible with your operating system
as well as the drive, and you must determine whether the
software shipped with the drive will do the job for you.
Third-Party Software
A large number of companies manufacture
backup software designed for different types of tape drives
and different uses. For example, many manufacturers design
their backup software to be compatible with most networks.
Others specialize in DOS and Windows backup software. Some
specialize in OS/2 software. Others are well-known among those
whose computers run in UNIX. You may need to ask a trusted
retailer or call the software company itself to determine
whether a particular type of software is compatible not only
with the tape drive you have chosen, but also with your
network and operating environment.
Often, third-party software is easier
to use than the software designed by a tape manufacturer. The
tape manufacturer's software may have an unfamiliar interface
or its commands may seem cryptic to you, even if you have used
backup software for years. It is not uncommon for tape
manufacturers to include inadequate or even incomplete
documentation for the backup software included with the drive,
although this is generally the case only with lower-cost
models. In such a case, you may be able to solve the problem
by purchasing third-party software.
Third-party software often does a
better job of data compression than the software designed by a
tape manufacturer. In addition, third-party software often
includes capabilities not included with the software bundled
with many drives. Some of the capabilities you might want to
look for include the following:
- Unattended backup scheduling.
Enables you to schedule a backup for a time when you won't
need to use your computer.
- Macro capability. Use when
selecting options and the files to back up.
- A quick tape-erase
capability. Use when erasing the entire contents of a
tape.
- Partial tape-erase
capability. Use when erasing only part of a
tape.
- Tape unerase capability. Use
when recovering erased data.
- Password-protect capability.
Enables you to protect backup data from access by
unauthorized persons.
You can find backup software
manufacturers by reading some of the many monthly computer
magazines, paying particular attention to their usability
reviews. Generally, if a backup software product gets good
reviews, works on a system configuration such as yours, and
has the features you need, it is worth the price you pay.
Removable
Storage Drives
The reason for the shortage of storage
space on today's PCs is easy enough to understand. Just take a
look at the sheer number and size of the files stored in the
two main directories used by Windows (usually C:\WINDOWS and
C:\WINDOWS\SYSTEM). The amount of disk space used by the files
in those two directories alone can quickly balloon to 80M or
more after you also install a few Windows applications. The
reason is simple: Nearly all Windows applications place files
in one of the Windows directories that the application will
use later. These files include those with extensions such as
DLL, 386, VBX, DRV, TTF, and many others. Similarly, Windows
NT, OS/2, and UNIX, as well as the software applications that
run in these operating systems, can require enormous amounts
of storage space.
The remainder of this chapter focuses
on some of the more advanced data storage options on the
market: removable media large-capacity storage drives. Some
removable media drives use media as small as a 3 1/2-inch
floppy disk, while others use media about the size of a 5
1/4-inch floppy.
These drives, whose capacities range
from 35M to 1G or more, offer fairly speedy performance, the
capability to store data or less frequently used programs on a
removable disk, and the capability to easily transport huge
data files--Computer Aided Drawing (CAD) files and
graphics files, for example--from one computer to another. Or,
you can use a removable media disk to remove sensitive data
from your office so that you can lock it safely away from
prying eyes.
NOTE: Removable media drives can
also be used to back up critical data from a hard drive.
However, the higher price of the media itself (disks or
cartridges) makes this use somewhat prohibitive.
TIP: There are literally dozens
of removable storage devices currently on the market. Be
sure to compare your chosen solution against the competition
before making a final purchase. Be especially wary of
missing statistics in press releases and product
packaging--manufacturers are apt to omit a specification if
their drive doesn't measure up to the
competition.
See Table 18.5 for a direct
comparison of the most popular removable drive technologies.
Types of
Removable Media Drives
There are two commonly used types of
removable media drives: magnetic media and optical media, also
called magneto-optical media. Magnetic media drives use
much the same technology used on a floppy disk or hard drive
to encode data for storage. Magneto-optical media drives
encode information on disk by using newer technology, which is
a combination of traditional magnetic and laser
technologies.
Magnetic media drives are considerably
faster than magneto-optical drives and offer similar
capacities. The Syquest magnetic media drives, for example,
offer 14ms average access times, compared to the 30ms (or
slower) access times of magneto-optical drives.
Magneto-optical drives can be more than twice as expensive as
magnetic media drives. If you have a great deal of data to
store, however, the comparative cost of using a
magneto-optical drive drops because magneto-optical media
cartridges are considerably less expensive than magnetic
media. For example, 10 270M Syquest cartridges can cost
roughly $80 each, and 150M Bernoulli cartridges can cost about
$90 apiece. The 128M magneto-optical cartridges can cost as
little as $25 apiece.
There are also several connection
options for the leading removable drives. Although SCSI has
been, and continues to be, a popular solution, many drives
today connect to the computer's parallel port. This option
allows one drive to be easily shared between several different
computers. Of course, internal SCSI and IDE solutions remain
just as popular for the single machine installation.
NOTE: Connection or installation
of removable media drives is very similar to connecting and
installing other internal and external
peripherals.
The installation of external parallel
port drives is generally straightforward, requiring a
special cable that comes with the drive and installation of
special software drivers. See the instructions that come
with each drive for the specifics of its installation.
The following sections provide
information on magnetic media and magneto-optical drive types.
Magnetic Media
Drives
A small group of companies dominate the
market for magnetic removable media drives. One company,
Iomega, always tops the list because it developed the first
popular large-capacity removable magnetic media drives, and
because its disk cartridges are known as the most rugged in
the industry. Two other leading names in removable magnetic
media drives are Syquest and 3M.
Removable magnetic media drives are
usually floppy or hard disk based. For example, the popular
Zip drive is merely a 3 1/2-inch version of the original
Bernoulli drive made by Iomega. The new 3M LS-120 drive stores
120M on a disk that looks exactly like a 1.44M
floppy!
Both the Bernoulli and Syquest designs
are their own de facto standard. Other manufacturers market
drives based on the Bernoulli and Syquest designs (and some
actually manufactured by Bernoulli or Syquest). For example,
the Jaz drive from Iomega uses a hard disk cartridge similar
to the Syquest. Generally these manufacturers' drives are
somewhat less expensive than the Bernoulli and Syquest models.
If you are considering one of these compatible drives,
however, make sure that the drive you are buying has the same
performance characteristics (average access speed, and so on)
as the original, and that the drive manufacturer offers the
same warranty as the original (Bernoulli, three years;
Syquest/SyDOS, two years).
Bernoulli Removable Media
Drives
The disk used in the Bernoulli drive is
roughly the same size as a 5 1/4-inch floppy disk, although a
large shutter, similar to the shutter on a 3 1/2-inch floppy
disk, easily differentiates Bernoulli disks from floppy disks.
Modern Bernoulli cartridges are available in 35M, 65M, 105M,
and 150M capacities. The Iomega Bernoulli MultiDisk 150 drive,
the company's newest model, reads and writes all of these
drive capacities. In addition, the MultiDisk reads and writes
to older Bernoulli 90M disks and reads older 40M disks. The
MultiDisk is available in both internal and external models.
Bernoulli disks are widely known as the
most durable of the removable media drive types. It is
probably safer to mail a Bernoulli cartridge than another type
of removable disk because the media is well-protected inside
the cartridge. Bernoulli encases a magnetic-media-covered
flexible disk (in effect, a floppy disk) in a rigid cartridge
in the same way the thin disk of a 1.44M floppy is encased in
a rigid plastic shell.
When it rotates in the drive, the disk
is pulled by air pressure towards the drive heads. Many people
do not think that there is head-to-disk contact in a Bernoulli
drive, but indeed there is. As the disk spins, the airflow
generated by the disk movement encounters what is called a
Bernoulli plate, a stationary plate designed to control
the air flow so that the disk is pulled toward the read/write
head. At full speed, the head does touch the disk, which
causes wear. Bernoulli drives have built-in random seek
functions that prevent any single track on the disk from
wearing excessively during periods of inactivity. Bernoulli
disk cartridges should be replaced periodically because they
can wear out. The disk itself spins at speeds approaching the
3,600 rpm of relatively slow hard drives. The drive has an
average seek time of 18ms, not a great deal slower than
today's medium-priced hard drives.
The Bernoulli MultiDisk 150 drive is
available in an internal model, which requires a half-height
drive bay, and an external model. The internal model connects
to the IDE hard drive adapter already installed in your
system. The external model requires a SCSI adapter card with
an external connector. The external model is powered by a
transformer that connects to a grounded AC wall
plug.
Another form of Bernoulli drive from
Iomega is the popular Zip drive. This device is available as a
external or internal SCSI unit and is also available as an
external parallel port device. The drive is capable of storing
up to 100M of data on a small removable magnetic cartridge
that resembles a 3 1/2-inch floppy disk, and has approximately
a 29ms access time and a 1M/sec transfer rate when used with a
SCSI connection. If the parallel connection is used, the
drive's speed is often limited by the speed of the parallel
port.
The Zip drives use a proprietary 3
1/2-inch disk made by Iomega. It is about twice as thick as a
standard 3 1/2-inch floppy disk. The Zip drives do not accept
standard 1.44M or 720K floppy disks, making this an unlikely
candidate for a floppy drive replacement. Zip drives have
become popular in use as an external drive for exchanging data
between systems, but the major PC manufacturers have not
recognized the proprietary format directly in the system BIOS
or in the operating system. The popularity and functionality
of the Zip drive has now been greatly exceeded by the new
LS-120 "floptical" drive introduced by 3M and Matsushita, and
supported by Compaq and other major PC manufacturers. More
information about the revolutionary LS-120 drive follows in
the next few sections.
Removable Media Hard Disk Drives
Syquest manufactures some drives that
use 5 1/4-inch cartridges and others that use 3 1/2-inch
cartridges. But the Syquest disks, like the Bernoulli
cartridges, are easily differentiated from floppy disks. The 5
1/4-inch 44M and 88M cartridges used in some SyDOS drives are
encased in clear plastic, as are the SyDOS 3 1/2-inch 105M and
Syquest 270M cartridges. The disk spins inside the cartridge
at several thousand rpm. Syquest claims a 14ms average access
time for the drives it manufactures.
The disks for the Syquest and SyDOS
drives are composed of a rigid platter inside a plastic
cartridge but are not as well-protected as the disk in a
Bernoulli cartridge. Some people consider these disks fragile.
If the Syquest and SyDOS cartridges are not severely jostled
or dropped, however, they can be transported safely. These
cartridges must be carefully protected when they are mailed or
shipped.
The Syquest/SyDOS drives are available
in internal and external models. The internal models require a
connection to the existing IDE hard drive interface card. The
external models require a SCSI interface card with an external
connector and are powered by a transformer that connects to a
grounded AC wall plug.
Another type of removable hard disk
drive is the Jaz drive from Iomega. This is physically
and functionally identical to the Syquest drives in that it is
a true removable cartridge hard disk, except the capacity of
the cartridge has been increased to 1G. Unfortunately, the
cartridges themselves cost about $100, which is about seven
times the cost of a DAT (Digital Audio Tape) cartridge that
stores four to eight times more data! The high cost of the
media makes the Jaz drive unsuitable for backup compared to
traditional tape media, but possibly useful as an add-on
external SCSI hard disk.
Magneto-Optical
Drives
Magneto-optical drives, which are
manufactured by a large number of companies, use an ingenious
combination of magnetic and laser technology to pack data on 5
1/4-inch and 3 1/2-inch disks contained in cartridges. The
media itself and the construction of the platter are similar
in ways to the media of a CD-ROM disc. An aluminum base is
covered with clear plastic, then a layer of magnetic,
optically active media particles--an alloy of cobalt, iron,
and terbium. A clear plastic coating seals the disk, rendering
it nearly impervious to shock, contamination, and
damage.
Although the magneto-optical disks are
similar to CD-ROM discs, there is a world of difference in the
way data is stored. When manufacturers write CD-ROM discs, the
laser actually burns pits into the media to represent the
data. These pits are read by the laser and translated into the
form of computer data. In the case of magneto-optical disks,
the magnetically/optically active media is not burned or
pitted. Instead, during the writing process a magneto-optical
drive focuses a laser beam onto a very tight track--a much
thinner track than could be used to store data on a purely
magnetic media platter. The laser beam heats the track, and a
weak magnetic signal is applied. The result is that only the
thin track of heated media receives the magnetic signal and
stores the data it contains.
Unlike a CD-ROM disc, a magneto-optical
disk theoretically can be rewritten an infinite number of
times because the media is never burned or pitted. When the
time comes to erase data from or rewrite the disk, the disk is
simply reheated with the laser and the old data is removed
magnetically so that new data can be recorded. When the
magneto-optical drive reads the disk, the drive functions
optically--that is, the laser reads the data from the disk
(without heating the media).
Because of the thin tracks on which
data is written to magneto-optical disks, the data is packed
extremely densely: Large amounts of data can be packed on a
platter about the same size as common 3 1/2-inch and 5
1/4-inch floppy disks. The current maximum capacity of the 3
1/2-inch cartridges is 230M; the 5 1/2-inch cartridges can
hold as much as 1G of data. It is important to note, however,
that capacity ratings of magneto-optical disks can be
misleading. Magneto-optical disks are double-sided, like
floppy disks, but magneto-optical drives have only one
read/write head. Therefore, to read or write to the second
side, you must manually flip over the cartridge. So only half
the disk capacity is available at any one time.
For many applications, magneto-optical
drives are tediously slow, although some drives--using
refinements of the basic magneto-optical technology--offer
data-access speeds that are inching more closely to those of
removable magnetic media drives. One reason that
magneto-optical drives are slow is that they typically spin
the disk at roughly 2,000 rpm--much slower than the 3,600 rpm
of a relatively slow hard drive. Another reason for the slow
speeds is that the read/write head mechanism, although
optically and magnetically advanced, is mechanically a kludge.
The massive mechanism of a magneto-optical drive's read/write
heads takes much longer to move and settle than the read/write
heads of a hard drive or even a removable magnetic media
drive.
Magneto-optical drives typically are
rated with average access speeds of about 30ms. However, these
average access speed figures do not tell the entire story. The
process of rewriting a disk can take nearly twice the time it
takes to read the disk. Because of the way magneto-optical
technology works, all the bias magnetic field of the area of
the disk to be written must be oriented in a single direction
during the write process. Because of this limitation, during
the write process most magneto-optical drives must make a
first pass over the disk to align the tracks of the disk that
are to be rewritten. Then the drive makes a second pass over
the disk to realign, or change the alignment of, the necessary
areas. This alignment/realignment process is known as
two-pass recording.
New magneto-optical technologies are
emerging which use single pass recording of disks. If speed is
an important factor in choosing a magneto-optical drive, you
should be prepared to pay extra for a drive whose performance
is not penalized by two-pass recording technology. In
addition, several manufacturers are offering drives that spin
the platter at speeds approaching the 3,600 rpm speeds of a
hard drive. The performance boost offered by these drives is
considerable, but this technology also boosts considerably the
prices of these drives.
Most manufacturers adhere to the
International Standards Organization (ISO) specifications for
magneto-optical disks and drives. The ISO standard calls for
all drives to use a SCSI host adapter to interface with the
computer. Under the ISO standard, 5 1/4-inch drives must be
able to read two different disk formats: disks with 512-byte
sectors and disks with 1,024-byte sectors. The disks with
512-byte sectors have a capacity of roughly 600M; those
1,024-byte sectors hold 650M of data. Under the ISO standard,
the 3 1/2-inch drives, which are quite popular among
first-time purchasers, are required to read only the 128M
disks.
Some manufacturers, in addition to
designing their drives to meet ISO standards, also design
their drives to use a proprietary data format that can
increase the capacity of 5 1/4-inch disks to about 1.3G. Both
5 1/4-inch and 3 1/2-inch drives are available as internal and
external units.
Comparing
Removable Drives
Deciding on a removable drive is
getting tougher with more than a dozen removable drives
currently on the market. Iomega and Syquest lead the pack, but
new entries from Exabyte and Avatar Peripherals provide their
own proprietary drives as well.
Table 18.5 shows a direct comparison
between the most popular removable drives on the market.
Table 18.5 Removable Drive
Specifications
Drive Type |
Drive Cost |
Disk/Cartridge Cost |
Disk/Cartridge Capacity |
Average Seek Time |
Data Transfer Rate |
Iomega Zip Parallel |
$149 |
$15 |
100M |
29ms |
1.4M/sec |
Iomega Zip SCSI |
$149 |
$15 |
100M |
29ms |
1.4M/sec |
Imation LS-120 Internal |
$179 |
$18 |
120M |
70ms |
4.0M/sec |
Syquest 235 Parallel |
$250 |
$30 |
235M |
13.5ms |
1.25M/sec |
Avatar Shark 250 Parallel |
$299 |
$30 |
250M |
12ms |
1.2 M/sec |
Avatar Shark PCMCIA |
$299 |
$30 |
250M |
12ms |
2.0M/sec |
Syquest 235 SCSI/IDE |
$299 |
$30 |
235M |
13.5ms |
2.4M/sec |
Iomega Jaz (SCSI) |
$399 |
$99 |
1G |
12ms |
5.4M/sec |
Avatar Shark iSeries IDE |
$30 |
250M |
12ms |
2.5M/sec |
|
Syquest Syjet SCSI |
$399 |
$99 |
1.5G |
12ms |
5.3M/sec |
Syquest Syjet IDE |
$399 |
$99 |
1.5G |
12ms |
5.3M/sec |
CD-R Drives |
$500-$1,000 |
$5 |
650M |
<150ms |
150K/sec-2.4M/sec |
When shopping for a removable drive,
keep the following in mind:
- Price per megabyte of
storage. Take the cost of the drive's cartridge or disk
and divide it by the storage capacity to see how much you
are paying per megabyte of storage. This difference in price
will become quite apparent as you buy more cartridges or
disks for the drive. (Don't forget to factor in the cost of
the drive itself!)
- Access time versus need of
access. The access and data transfer speeds are only
important if you need to access the data frequently or
quickly. If your primary use is archiving data, a slower
drive may be fine. However, if you plan on running programs
off of the drive, choose a faster drive
instead.
- Compatibility and
portability. Opt for an external SCSI or parallel port
solution if you will need to move the drive between various
computers. Also verify that the drive has drivers available
for each type of machine you want to connect the drive to.
Write-Once, Read
Many (WORM) Drives
The removable media drive known as
write-once, read many (WORM) is designed to serve as a
nearly bulletproof data archival system. If you have extremely
important data files that absolutely must remain in an
unaltered state--perhaps accounting or database data--a WORM
drive can provide the kind of security you are looking for.
Data written to a WORM disk cannot be changed.
The WORM disk is encased in a
high-impact cartridge with a sliding shutter similar to the
shutter on a 3 1/2-inch floppy disk. The cartridge and the
extremely durable nature of the disk inside make WORM disks
worry free for data exchange. A WORM drive cartridge is very
difficult to damage. The disk itself, with the media
sandwiched in plastic, is not unlike a CD-ROM disc or a
magneto-optical disk. The technology used to write a WORM
disk, however, is more like the technology used for CD-ROM
recording than that used for writing to magneto-optical disks.
The WORM drive uses a laser to burn microscopic patches of
darkness into the light-colored media.
A number of companies manufacture WORM
drives but follow no single standard. Therefore, a WORM disk
written on one manufacturer's drive is quite unlikely to be
readable on another manufacturer's drive. Each manufacturer
(sometimes small groups of manufacturers) uses its own
proprietary data format and disk capacity, and many use a
cartridge size only their drives can handle. For example, most
WORM drives are designed for 5 1/4-inch cartridges but some
WORM drives handle only 12-inch disks. In addition, although
most WORM drives interface the computer via SCSI host adapter,
others use different interfaces, some of them
proprietary.
Certainly, at least in part because of
these incompatibility problems, WORM drives are not big
sellers. No more than several thousand are sold each year at
prices soaring to the heights--some 5 1/4-inch drives cost
several thousand dollars. The 5 1/4-inch-drive cartridges,
which range in capacity from 650M to 1.3G, can cost more than
$180.
The term niche market is used
occasionally to describe a computer product or peripheral that
lacks broad appeal or usefulness. Because of its cost and
incompatibility problems, WORM drive technology is a niche
market product. Unless you must be able to store massive
amounts of data and ensure it can never be altered, you are
better off buying a magneto-optical drive, or perhaps even a
tape backup drive.
Compact Disc
Recordable (CD-R) Drives
Note that a variation on WORM
technology is also found in CD-R (CD-Recordable)
drives. CD-R drives are indeed WORM; however, they use a
special recordable CD-ROM disc that, once recorded, can be
played back or read in any standard CD-ROM drive. CD-R drives
are very useful for creating master CDs, which can be
duplicated for distribution within a company.
CD-ROMs, as you will remember from
Chapter 17, "CD-ROM Drives," work by reading the light
reflected by a laser striking the surface of the disc. Light
is either returned from the disc, or not. CD-R recorders work
by using a laser to etch a pattern into the raw media, leaving
places where light is reflected or not reflected.
NOTE: Because of the technical
changes in the way the media is made, there can be some
problems reading CDs made by CD-R devices in a standard
CD-ROM player. Most of these problems just result in poor
play performance as the CD-ROM tries to align itself to the
CD. However, some very old CD-ROM players can't handle CD-R
media.
CD-R Drive History
CD-R drives were originally used to
pre-master CDs prior to production of massive quantities by a
CD manufacturing facility. The CD-R drive was used to create a
few (normally less than 20) CDs that would then be tested to
make sure that the program worked or was installed correctly.
Then three of the CDs would be sent to the manufacturing
facility to be mastered and printed into thousands of
CDs.
Writing a CD with a CD-R Drive
CD-R drives generally come in slower
speeds than their CD-ROM reader counterparts. The fastest CD-R
drives write at 4x normal speed--given the system performance
to do so. However, some can read at up to 6x normal speed.
Whenever a CD-R is writing data, it is
making one long spiral on the CD, alternating on and off to
etch the pattern into the raw media. Because the CD-R can't
realign itself like a hard drive, once you start writing, you
must keep writing until you're finished with the track, or you
will ruin the CD.
You'll recall from Chapter 17 that the
normal speed for a CD is 150K/sec. When writing at a 4x speed,
the computer must provide data to the CD-R drive at 600K/sec.
If the computer isn't able to maintain that data rate, you'll
receive a Buffer under-run message.
The Buffer under-run message
indicates that the CD-R had to abort recording because it ran
out of data in its buffer to write to the CD. This is the
biggest problem that people have with CD-R devices. Providing
a fast source to write from--usually a fast SCSI drive--on a
system with plenty of RAM will generally help avoid buffer
under-run.
CD-R Software
Another difficulty with CD-R devices is
that they require special software to write them. Where most
removable drives can be used immediately by built-in drives,
the CD-R drive must have special CD-ROM burning software.
This software handles the differences
between how data is stored on a CD and how it is stored on a
hard drive. As you learned in Chapter 17, there are several
CD-ROM standards for storing information. The CD-ROM burning
software arranges the data into one of these formats so the CD
can be read by a CD-ROM reader.
It used to be that CD-ROM burning
software required that all of the files on the hard drive be
arranged into a single file which was then written to the CD.
The single file contained all of the sectors on the CD, which
means every file, all of the directory information, plus the
volume information. This single file took as much space as the
files being placed on the CD. The result was that you had to
have about 1.5G of storage to burn a single CD (650M/CD x 2 =
1.3G + overhead~~1.5G).
This is no longer a requirement as most
software supports virtual images. The software assembles the
directory information and burns it to the CD, then opens each
file on the CD and provides the data directly from the
original file. This works well, however, because the files are
not sequentially located on the hard drive; it must seek
track-to-track, which takes longer. As a result, some slower
hard drives may not be able to keep up with writing at the
maximum 4x rate supported by some drives.
Most software and CD-R drives support a
simulate recording mode which performs the same actions as in
a normal writing mode; however, the laser isn't powered up to
a level to etch the disc. This is useful in testing the
performance of your complete system, and if it can't handle
the data rate, you don't waste a CD.
CD-R as Mass Storage
CD-R costs are unique when considering
a form of mass storage. Most mass-storage mediums enable you
to rewrite on the media over and over, and although there is a
new breed of CD-R drives called CD-RW which support
rewriting a CD, most don't.
Each CD-R CD can be found for less than
$5 in quantities of 25 or above. Most other storage mediums
have a much greater media cost. Even at deeply discounted
pricing, your DAT, 8mm, QIC, or DLT tapes can cost between
$20-$100. Removable media costs can range from
$75-$300.
Even though tapes store more and their
cost per megabyte is much smaller, accessing files on tape can
be a time-consuming process. Removable media is generally more
expensive and requires that the recipient have the same kind
of drive, or the drive must be transported with you when
trying to shuttle files from one place to another.
Compared with either tape or other
removable media, using a CD-R to burn CDs can be very
cost-effective and easy when transporting large files or
making archival copies. Another benefit of the CD for making
archival copies is that CDs have a much longer shelf life than
tapes or removable media.
However, CD-R isn't a very effective
backup medium because the CD can only be written once. Because
you can't reformat and reuse the CDs, subsequent backups make
previous discs disposable at best.
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