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.
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).
Following are some CacheFS terms that will be used in this
chapter:
- back file system
The file system that is being cached. On HP-UX 10.20,
NFS is the only supported back file system.
- front file system
The file system that contains the cached data. On
HP-UX 10.20, HFS and JFS are the supported front file systems.
- cold cache
A cache that does not yet have any data in its front
file system. In this case, requested data must be copied from the
back file system to the front file system (that is, the cache must
be populated). An attempt to reference data that is not yet cached
is called a "cache miss."
- warm cache
A cache that contains the desired data in its front
file system. In this case, the cached data can be returned to the
user without requiring any action from the back file system. An
attempt to reference data that has been cached is called a "cache
hit."
Printable version
