NFS Services Administrator's Guide (B.11.31.02) January 2008

Notes on Configuring Replicated Servers
Directories with multiple servers must be mounted as read-only to ensure that the versions
remain the same on all servers.
The server selected for the mount is the one with the highest preference, based on a sorting order.
The sorting order used gives highest preference to servers on the same local subnet. Servers on
the local network are given the second strongest preference. As a result, 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 preferred. For multiple servers outside the local network, and with no weighting factors
assigned, the server with the lowest response time is used for the mount.
Multiple servers provide users with reliable access to a mounted directory. 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 is mounted from the server that is not busy.
If the list of multiple servers contains a combination of servers that includes all versions of the
NFS protocol, then AutoFS selects 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.
Including a Map in Another Map
If you want your map to refer to an external map, you can do so by including the external map
in your map. The entries in the external map are read as if they are part of your map.
To include the contents of an AutoFS map in another AutoFS map, add a plus (+) sign before the
map name, as in the following example:
# /etc/auto_home file
# local mount-point mount options remote server:directory
basil -nosuid basil:/export/home/basil
+auto_new
Assume that the /etc/auto_home map is listed in the master map with the following line:
/home /etc/auto_home
If a user, whose home directory is in /home/basil, logs in, AutoFS mounts the
/export/home/basil directory, from the host, basil.
If a user, whose home directory is in /home/sage, /home/thyme, or any subdirectory of /home
other than basil, logs in, AutoFS consults the auto_home map for information on mounting
the user’s home directory.
The plus (+) sign instructs AutoFS to look up a different map for the information it needs to
mount the directory. If the map name following the plus sign begins with a slash, AutoFS assumes
that it is a local file. If the map name contains no slashes, AutoFS uses the Name Service Switch
to determine whether it is a file, NIS map, or an LDAP map.
You can include an AutoFS map inside a local file, but not inside an NIS or LDAP map.
For more information on including a map in another map, see automount(1M).
Creating a Hierarchy of AutoFS Maps
Hierarchical AutoFS maps provide a framework that enables you to organize large exported
filesystems. Together with NIS, which allows you to share information across administrative
domains, hierarchical maps enable you to decentralize the maintenance of a shared namespace.
78 Configuring and Administering AutoFS