NFS Services Administrator's Guide (5900-1632, August 2011)

4 Configuring and Administering a Cache Filesystem
This chapter introduces the Cache Filesystem (CacheFS) and the CacheFS environment. It also
describes how to configure and administer CacheFS on a system running HP-UX 11i v3.
This chapter addresses the following topics:
• “CacheFS Overview” (page 79)
• “CacheFS Terms” (page 79)
• “How CacheFS Works” (page 80)
• “Features of CacheFS” (page 80)
• “Configuring and Administering CacheFS” (page 82)
• “Using CacheFS” (page 90)
• “Common Problems While Using CacheFS” (page 91)
CacheFS Overview
CacheFS is a general purpose filesystem caching mechanism that improves NFS client and server
performance. CacheFS client performance is improved by caching data to a faster local filesystem
instead of going over the wire to a slow server or on a slow network. This results in reduced server
and network load because the clients send fewer requests to the server.
In an NFS environment, CacheFS:
• performs local disk caching of filesystems which enables the client systems to become less
reliant on the server
• improves performance of clients on slow networks
• increases the number of clients that can be supported by a single server
• decreases the overall server load which can result in better server performance.
When data is read from a cached NFS-mounted filesystem for the first time, it results in some
overhead when CacheFS writes the data to its local cache. After 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 NFS write performance.
Therefore, good candidates for cached filesystems include manpages and executable programs,
which are read multiple times though rarely modified.
By default, CacheFS maintains consistency between the cached filesystem and the remote filesystem,
using a consistency checking model similar to that of standard NFS (polling for changes in file
attributes).
NOTE: CacheFS cannot be used with NFSv4.
CacheFS Terms
The following CacheFS terms are used in this chapter:
back filesystem A filesystem that is cached is called a back filesystem. HP-UX currently
supports only NFS as the back filesystem.
front filesystem A local filesystem that is used to store the cached data is called a front
filesystem. HFS and VxFS are the only supported front filesystem types.
cold cache A cache that has not yet been populated with data from the back
filesystem is called cold cache.
cache miss An attempt to reference data that is not yet cached is called a cache
miss.
CacheFS Overview 79