Configuring Replicated Servers for an AutoFS Directory

This section describes how to configure multiple replicated servers for an AutoFS directory.

To configure multiple replicated servers for a directory, follow these steps:

Follow the instructions in “Automounting a Remote Directory Using a Direct Map” or “Automounting a Remote Directory Using an Indirect Map” to automount the direct or indirect map.
In the direct or indirect map, modify the line that mounts the remote directory so that it lists multiple servers.
- If the remote directory has the same name on every server, use a syntax such as the following example from an indirect map:
  man -ro broccoli,cabbage,cauliflower:/usr/share/man
- You can assign a weighting factor to the servers, by specifying a number in parentheses after each server name. The lower the weighting number, the more likely the server is to be selected.
  man -ro \ broccoli(1),cabbage(2),cauliflower(3):/usr/share/man
  Servers with no weight factor specified have a default weight of zero and are most likely to be selected.
  However, server proximity is more important than the weighting factor 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 weight you assign. The weighting factor is taken into account only when choosing between servers with the same network proximity.
- If the remote directory has a different name on different servers, use a syntax such as the following from a direct map:
  /nfs/proj2/schedule -ro \ broccoli:/export/proj2/schedule, \ cauliflower:/proj2/FY07/schedule
  AutoFS reads this entry as one line. The line is broken for readability, and the backslash (\) instructs AutoFS that the line continues after the line break.
Create and configure the /etc/netmasks file. AutoFS requires the /etc/netmasks file to determine the subnets of local clients in a replicated multiple server environment.
The /etc/netmasks file contains 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. For standard subnetting, the file must contain a single line for each network providing the network number and the network mask to use on that network. Specify the network number and mask using the conventional IP dot (.) notation. The network number must be a class A, B, or C network number. For example:
network number netmask
128.32.0.0 255.255.255.0
For variable length subnetting, the /etc/netmasks file must contain a line for each subnet where the first field is the subnet and the second field is the netmask. The format for specifying these fields is the same as that of standard subnetting.

Example of using the /etc/netmasks File

The following example shows how AutoFS uses the /etc/netmasks file to determine the local client subnets in a multiple-server environment. In this example, servers sage and thyme export or share /nfs/mount. The IP address for server sage is 15.43.232.30, and the IP address for the server, thyme is 15.244.10.20:

# /etc/auto_direct file

/nfs_mount sage,thyme:/nfs/mount

#/etc/netmasks file on the client basil:

#network number netmask

15.43.234.210 255.255.248.0

AutoFS uses the /etc/netmasks file and determines that the masked value for the subnet of sage and the network number is the same (15. 42. 232. 0). This shows that the client is on the same network as sage. AutoFS then mounts /nfs/mount from sage on the local subnet.

Notes on Configuring Replicated Servers

Directories with multiple servers must be mounted read-only, to ensure that the versions remain the same on all the servers.

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 network 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. For multiple servers outside the local network, and with no weighting factors specified, the server with the lowest response time is used for the mount.

Multiple servers give users reliable access to a mounted directory, because if one server is down, the directory can be mounted from another. Moreover, multiple servers provide some load balancing across the network; a server that is not busy responds more quickly to an AutoFS poll than one that is heavily loaded. The directory will be mounted from the server that is not busy.

If the list of multiple servers contains a combination of servers using all versions of the NFS protocol, then AutoFS chooses a subset of servers with the highest NFS protocol version configured. For example, a list contains a number of servers configured with the NFSv4 protocol, and a few servers configured with the NFSv2 protocol. AutoFS will use the subnet of servers configured with the NFSv4 protocol, unless a server configured with the NFSv2 protocol is closer.

Configuring Replicated Servers for an AutoFS Directory

Technical documentation

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Example of using the /etc/netmasks File

Notes on Configuring Replicated Servers