AIX Version 4.3 Differences Guide

Creating the Local Cache File System
A local cache file system is created by using the cfsadmin command with the -c
flag, as shown in the following steps:
1. Login as root.
2. Create a cache using the -c flag of the cfsadmin command
# cfsadmin -c -o
where parameters specify resource parameters, and cache-directory is the
name of the directory where the cache should be created. A list of
configurable parameters is shown in Table 40 on page 185. Although the
cache is referred to as a cache filesystem, it is not a filesystem in the true sense.
It is, in fact, a cache directory, which resides on a normal JFS. For this reason,
if you are creating a large cache filesystem, it is advisable to create a
dedicated JFS to be used for this purpose. This is because the cache
filesystem is created with parameters that indicate the percentage of the
underlying filesystem it is allowed to use.
3. Mount the back file system in the cache
# mount -V cachefs -o backfstype=nfs,cachedir=/ \
remhost:/
where remhost:/ is the name of the remote host and file
system where the data resides, and is the mount point on
the client where the remote file system should be mounted.
CacheFS can also be administered using SMIT.
Cached File Systems Consistency Checking
To ensure that the cached directories and files are kept up to date, CacheFS
periodically checks consistency of files stored in the cache. To check consistency,
CacheFS compares the current modification time to the previous modification
time. If the modification times are different, all data and attributes for the directory
or file, are purged from the cache, and new data and attributes are retrieved from
the back file system.
When a user requests an operation on a directory or file, CacheFS checks if it is
time to verify consistency. If so, CacheFS obtains the modification time from the
back file system and performs the comparison.
Note: It is important to remember that CacheFS is intended to be used as a
mechanism for reducing network and server workload. Because the remote file
system data is held locally on the client, and consistency is only checked at
intervals, it means that the data on the server can change, and the client is
unaware of this for a period of time. You should, therefore, only use it for
read-only, or read-mostly, file systems where the file system contents do not
change rapidly.
One example where CacheFS would be suitable is in a CAD environment where
master-copies of drawing components can be held on the server and
cached-copies kept on the client workstation when in use.
184 AIX Version 4.3 Differences Guide