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Complete Idiot's Guide to Linux
(Publisher: Macmillan Computer Publishing)
Author(s): Manuel Ricart
ISBN: 078971826x
Publication Date: 12/22/98

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Write-Once CD-ROMs

New technology and price drops have made the CD-R a popular choice with multimedia enthusiasts. The CD-Rs use a technology similar to a regular CD, but instead of being ”pressed,” they are burned using a process similar to MO disks. CDs created by CD-Rs are not as rugged as pressed CDs, but they will last far into the future if you take care of the disk. These disks are compatible with any desktop system that has a CD-ROM, which has helped in making this a popular write once-read many (WORM) format. Current capacity is about 600MB. Recording speed is slow—typically 2–8X speed, whereas most CD-ROMs can read at speeds up to 32X. New formats for CD-ROMs that are currently in the works will yield 17GB of storage, making them a very interesting solution to backup and archival tasks.

Rewritable CD-ROMs

The popularity of CD-Rs helped pave the way for a newer medium to emerge: the CD-RW. Based on the same technology for the CD-R, CD-RWs are a medium that can be reused, much like a floppy disk. The material the medium is made from and the drives used with CD-RWs is different from the standard CD-R, but the process is basically the same concept.

Iomega Jaz and Zip Drives

Zip is a popular removable disk drive. They are very inexpensive: around $150 for the drive and $10–$15 per disk. Each disk holds about 100MB. They are available in SCSI(small computer systems interface—pronounced “skuzzy”), parallel, and combination flavors.

The SCSI drives require a SCSI interface (a special type of disk controller, or host adapter as they are called, that uses standardized commands for accessing the hardware).

Jaz drives are a higher-performance, higher-capacity version of the Zip drives. Jaz drives are a bit more expensive, about $350, and require a SCSI interface. Disks cost more than $99 and pack 1GB+ of fast storage space. This is a hot product.

Nine-Track Magnetic Tapes

This is an old format of tape written at 800, 1600, or 6250BPI (bits per inch) density. This format is not in great use today except by old mainframes. Some programs such as dump, a backup program, use this format as a basis for their tape capacity calculations.

4mm Digital Audio Tapes

The DAT, which stores 1.3GB of information on a 60-meter tape (1.95GB on a 90m and 2.6GB on a 120m), was originally designed for the audio market. Digital data storage (DDS), the computer version of DAT, provides the smallest storage solution of all. Its capacity is typically more than doubled by the use of compression. Drives with hardware compression can store up to 8GB. The preferred tape backup system is DDS for most UNIX users. These drives, many of which can be had for about $400, require a SCSI interface. This is the type of tape drive that I have on my own setup, and it is great!

8mm Cartridge Tapes

8mm cartridges (also known as “Exabytes,” for the only company that manufactures them) are the same size as their video counterparts. Many administrators purchase high-quality “video grade” tapes instead of the premium data versions. Drives can store 2–5GB, and current versions can pack up to 40GB into a single tape at a blazing 360MB per minute write speed. Because fewer tapes are needed, this is a very convenient format, especially for server systems. 8mm drives are commonly found in multidrive libraries for storage capapcity exceeding 300GB.

DLT Cartridge Tapes

DLT, or digital linear tape, was originally pioneered by Digital Equipment Corporation, and was used for ages on large VAX servers. The first DLT drives stored 40-60MB, but were proven to be some of the most reliable magnetic storage media ever, in part thanks to their .50 in (half-inch) tape width and linear data path.

Current DLT tape drives store up to 70GB compressed at a rate of 300MB per minute. Like 8mm drives, DLT drives are often found in ultra-high capacity storage libraries. Desktop models are available for the prestige-conscious desktop user, however.

What to Back Up

Typically, you don’t need to back up the entire system, as a good amount of the stuff on your disk (at least initially) you already have as part of your installation CD. This provides you with a twofold benefit: Your backups will be smaller (because there is less stuff to back up), and they will go faster (again as a result of the reduced data). Linux offers good organization of important configuration files that are typically kept in a common place. As you configure and change your system, you should maintain a log (a simple account to which you can send an email message can make a simple but effective way of documenting changes you perform to your system) and use it to drive your backup strategy. At the very least, you should back up these directories:

  /etc
  /usr/lib
  /usr/X11R6/lib/X11 (if you use X Windows)
  /usr/src/linux (if you have modified your kernel sources)
  /home
  /var/spool/mail

It’s important to back up these directories because they contain system configuration files, user files, and user mail spool directories. Given the low cost of tape drives today, you probably ought to invest in one. The capacity should match the size of the hard disk you have. Although spawning a backup onto multiple tapes is a very common thing, there’s nothing worse than a missing tape or a tape gone bad. By putting all your data onto one tape, you know you have it, and you don’t have to worry about partial backup issues.

Simple Backups

A simple backup is one in which you copy your files onto another medium. There isn’t a strategy, so it is simple to do—provided you know what you want to save. You can use the cp command to copy the files, or you can use an archiving tool such as tar, which I describe next.


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