NFS Services Administrator's Guide

Configuring and Administering a Cache Filesystem
CacheFS Overview
Chapter 4 149
CacheFS Overview
The Cache FileSystem (CacheFS) is a general purpose filesystem caching
mechanism that improves client performance when dealing with slow
NFS servers. By caching data to a faster local filesystem, instead of going
over the wire to a slow server or a slow network, the CacheFS client sees
much better performance. This results in reduced server and network
load as the clients are sending fewer requests to the server because they
already cached a copy of the data. This in turn improves NFS server
performance.
In an NFS environment, CacheFS increases the number of clients
supported by a single server, reduces server and network loads, and
improves performance of clients on slow links such as PPP. CacheFS also
performs local disk caching of filesystems, which reduces the network
traffic. The individual client systems become less reliant on the server.
This decreases the overall server load and results in better server
performance.
Good candidates for cached filesystems include manpages and executable
programs, which are read multiple times but rarely modified. Using
CacheFS for a directory that is modified frequently, such as /var/mail,
is not an optimal use of resources.
By default, CacheFS maintains consistency with the cached filesystem
using a consistency checking model such as NFS (polling for changes in
file attributes).
The first time data is read from a cached NFS-mounted filesystem, it
results in some overhead when CacheFS writes the data to its local
cache. Once the data is written to the cache, read performance for the
cached data improves significantly. CacheFS improves read performance
for data that is read more than once. However, it does not improve the
write performance.
NOTE CacheFS cannot be used with NFSv4. If NFSv4 is enabled by default,
CacheFS mounts fail. However, the CacheFS mount succeeds if you
specify the NFS version as either version 2 or version 3.