NFS Performance Tuning for HP-UX 11.0 and 11i Systems

nfs performance tuning for hp-ux 11.0 and 11i systems page 81

Notes:

Page 81July 22, 2002

cachefs

CacheFS Limitations (part 2)

• Only certain files survive a CacheFS unmount or reboot

• Any file marked “un-cacheable” will be removed

Ø Writing to a cached file marks the file “un-cacheable”

Ø When a cache reaches its configured disk space or inode usage

thresholds, the LRU algorithm will select files to remove.

Ø Every cached file is represented by a 32-slot allocation map

data structure, where each slot represents a non-contiguous

chunk of the file. Any file that requires more than 32 non-

contiguous chunks to be loaded is considered “un-cacheable.”

There are three main reasons CacheFS will disable caching for a file:

• When a process on the NFS client writes to the cached file

• When a cache reaches its configured disk space or inode usage thresholds, the

LRU algorithm will select files to remove from the cache

• When 33 or more non-contiguous chunks of the cached file are referenced

Once a file is flagged as “un-cacheable,” any read requests for this file must be

serviced by the back (NFS) filesystem, effectively nullifying any CacheFS benefits

for this file. All files that have been marked “un-cacheable” are removed from the

cache directory when the CacheFS filesystem is unmounted or the NFS client system

is rebooted.