System information

File systems that support functionalities required by FS-Cache cache back-end include the Red Hat

Enterprise Linux 6 implementations of the following file systems:

ext3 (with extended attributes enabled)

ext4

BTRFS

XFS

The host file system must support user-defined extended attributes; FS-Cache uses these attributes to

store coherency maintenance information. To enable user-defined extended attributes for ext3 file

systems (i.e. device), use:

# tune2fs -o user_xattr /d ev/device

Alternatively, extended attributes for a file system can be enabled at mount time, as in:

# mo unt /d ev/device /path/to/cache -o user_xattr

The cache back-end works by maintaining a certain amount of free space on the partition hosting the

cache. It grows and shrinks the cache in response to other elements of the system using up free

space, making it safe to use on the root file system (for example, on a laptop). FS-Cache sets defaults

on this behavior, which can be configured via cache cull limits. For more information about

configuring cache cull limits, refer to Section 10.4, “ Setting Cache Cull Limits” .

Once the configuration file is in place, start up the cachefi l esd daemon:

# servi ce cachefi l esd start

To configure cachefi l esd to start at boot time, execute the following command as root:

# chkco nfi g cachefi l esd o n

10.3. Using t he Cache Wit h NFS

NFS will not use the cache unless explicitly instructed. To configure an NFS mount to use FS-Cache,

include the -o fsc option to the mo unt command:

# mo unt nfs-share: / /mount/point -o fsc

All access to files under /mount/point will go through the cache, unless the file is opened for direct

I/O or writing (refer to Section 10.3.2, “ Cache Limitations With NFS” for more information). NFS

indexes cache contents using NFS file handle, not the file name; this means that hard-linked files

share the cache correctly.

Caching is supported in version 2, 3, and 4 of NFS. However, each version uses different branches

for caching.

10.3.1. Cache Sharing

There are several potential issues to do with NFS cache sharing. Because the cache is persistent,

blocks of data in the cache are indexed on a sequence of four keys:

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