Overview of the Cache File System

	IMPORTANT: CacheFS is not available on HP-UX 11.0.

The Cache File System (CacheFS) is a general purpose file system caching mechanism that improves NFS server performance and scalability by reducing server and network load. CacheFS provides the ability to cache one file system on another.

In an NFS environment, CacheFS increases the client per server ratio, reduces server and network loads, and improves performance for clients on slow links (for example, PPP).

CacheFS performs local disk caching of file systems, which reduces the network traffic. Individual client machines become less reliant on the server, thereby decreasing overall server load, which leads to an increase in server performance.

CacheFS improves read performance for data that will be read more than once. It does not improve write performance at all.

Good choices for cached file systems include man pages and executable programs, which are read multiple times and rarely modified. Using CacheFS for /var/mail is not a good use of resources. The /var/mail file is modified frequently and is typically read only once and then thrown away.

By default, CacheFS maintains consistency with the back file system using a consistency checking model like that of NFS (polling for changes in file attributes).

The first time data is read from an NFS-mounted file system, there is actually some overhead while CacheFS writes the data to its local cache. After the data is written to the cache, read performance for the file system is significantly improved.