Configuring Multiple Servers for an AutoFS Directory

To configure multiple (replicated) servers for an AutoFS directory, perform the following steps:

Follow the instructions mentioned in “Using a Direct AutoFS Map” or “Using an Indirect AutoFS Map”.
In the direct or indirect map, modify the line that mounts the remote directory so that multiple servers are listed.
- If the remote directory has a different name on different servers, use a syntax like the following example from a direct map:
  /nfs/proj2/schedule -ro \ broccoli:/export/proj2/schedule\ cauliflower:/proj2/FY94/schedule
  AutoFS reads this entry as one line. The line has been broken for readability, and the backslash (\) character indicates that the line continues after the line break.
- If the remote directory has the same name on every server, use a syntax like the following example from an indirect map:
  man -ro broccoli,cabbage,cauliflower:/usr/share/man
- You can assign weights to the various servers by specifying a number in parentheses after each server name. If the weight number is lower, the server is more likely to be selected.
  man -ro\ broccoli(1),cabbage(2),cauliflower(3):/usr/share/man
  Servers with no weight specified have a default weight of zero (most likely to be selected).
  Server proximity is more important than the weights you assign. A server on the same network segment as the client is more likely to be selected than a server on another network segment, regardless of the weights you assign. The weight has effect only when selecting between servers with the same network proximity.
AutoFS needs the /etc/netmasks file to determine the local client’s subnets in the replicated servers environment. You must manually create and configure the /etc/netmasks file for the replicated servers functionality to work properly.
The /etc/netmasks file contains Internet Protocol (IP) address masks with IP network numbers. It supports both standard subnetting as specified in RFC 950 and variable length subnetting as specified in RFC 1519. When using the standard subnetting, there should be a single line for each network with the network number and the network mask to use on that network. You can specify the network number and mask in the conventional IP ‘.’(dot) notation. The network number is restricted to be a class A, B, or C network number.
Consider the following example:
# network number netmask
128.32.0.0 255.255.255.0
The format is identical for variable length subnetting. However, there should be a line for each subnet with the first field being the subnet and the second field being the netmask.
The following example shows how AutoFS uses the /etc/netmasks file to determine the local client’s subnets in the replicated servers environment. In this example, the sage and thyme servers export /nfs/mount. The IP address for the sage server is 15.43.232.30, and the IP address for the thyme server is 15.244.10.20.
# /etc/auto_direct file
/nfs/mount sage,thyme:/user
#/etc/netmasks file on the client basil:
#network number netmask
15.43.234.210 255.255.248.0
AutoFS uses the /etc/netmasks file to determine the local client’s subnets and mounts /nfs/mount from the sage server on the local subnet.

To ensure that versions remain the same on all the servers, you need to mount directories with multiple servers as read-only.

The server chosen for the mount is the one with the strongest preference based on a sorting order. The sorting order used gives strongest preference to servers on the same local subnet; servers on the local net are given the second strongest preference. Therefore, if you configure multiple servers on both sides of a gateway, a server on the same side of the gateway as the NFS client is always used.

Among servers that are equally far away, response time determines the order, if no weighting factors are used. Multiple servers give users reliable access to a mounted directory because if one server is down, the directory can be mounted from another. In addition, multiple servers provide some load balancing across the network; a server that is not busy responds more quickly to AutoFS poll than the one that is heavily loaded. Therefore, the directory is mounted from a server that is not busy.

If the list of multiple servers contains some servers using the NFS Version 2 Protocol and some servers using the NFS Version 3 Protocol, AutoFS chooses a subset of the list having only servers with the same protocol. This subset is formed of servers using the NFS Version 3 Protocol, unless there are no such servers on the list, or there is a server using NFS Version 2 Protocol that has the strongest preference.

Configuring Multiple Servers for an AutoFS Directory

Technical documentation

» Table of Contents

» Index