NFS Services Administrator's Guide

Configuring and Administering AutoFS
Configuring Replicated Servers for an AutoFS Directory
Chapter 3132
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.