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.