Specifying redundant servers
Redundant servers
can be specified in either a direct or indirect map. In
both cases, multiple servers are specified in the
``location'' field of a map entry.
In the direct mount example in
Figure 13-1, ``An example of direct mounting using automount'',
instead of specifying just london as the remote
server for /usr/man, it is possible to specify
remote servers madrid and oslo, as
well.
The resulting direct map could look like:
/usr/man -r,soft london:/usr/man \ madrid:/usr/man \ oslo:/usr/manThis means that the mounting can be done from any of the specified locations (london, madrid, or oslo). This list can also be expressed as a list of servers (separated by commas and followed by a colon) and the pathname (as long as the pathname is the same for all of the specified servers), for example:
/usr/man -r,soft london,madrid,oslo:/usr/manThe first server to respond to the RPC ping issued by automount is selected, and an attempt is made to mount from it. The list does not imply an ordering, although servers on the local network will be contacted first.
This redundancy, which is very useful in an environment where individual servers may or may not be exporting their filesystems, exists at mount time only. There is no status checking of the mounted-from server by automount once the mount occurs. If the server goes down while the mount is in effect, the filesystem becomes unavailable. An option here is to wait the default five minutes until the auto-unmount takes place and try again. Next time around, automount chooses one of the other, available servers. Another option is to use the umount command, inform automount of the change in the mount table (as specified in the section ``Stopping and restarting automount''), and retry the mount.
See also: