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

nfs performance tuning for hp-ux 11.0 and 11i systems page 71

Notes:

Page 71July 22, 2002

Automounter Performance

Considerations (part 1)

• Default unmount timer and its effect on client caching

Ø Any buffer cache or page cache memory pages associated with

the filesystem are invalidated during an unmount attempt – even

if the unmount fails because the filesystem is busy (i.e. in use)

Ø Executable binaries, libraries, and any application data loaded

across an NFS mount will be discarded during a failed unmount

automount

autofs

Recommendation

Ø Use “-tl” (automount) or “-t“ (AutoFS) to increase unmount timers

Ø Use AutoFS direct maps – uses reference timers to avoid unmounts

A very important reason to consider using a longer automount unmount timeout

value is to avoid a nasty side-effect that occurs when unmounting an NFS filesystem

on HP-UX systems – all buffer cache and page cache memory pages associated

with the filesystem being unmounted are invalidated. This occurs whether the

filesystem is in use or not, regardless of whether the unmount attempt is successful

or not. This means that both executable binaries and libraries that have been

loaded across an NFS mount (page cache), as well as any application data (buffer

cache) for an NFS mount will be discarded during an unmount attempt – even if the

unmount fails. The NFS client is then required to re-read these pages from the

server.

The command-line options used to set the unmount timer value differs between

automount and AutoFS – automount uses “-tl” and AutoFS uses the “-t” option. Both

options specify the number of seconds between unmount attempts. The appropriate

number for this timeout value is largely dependent upon the client’s usage patterns

for the filesystems it mounts. In some environments a reasonable starting value

would be 8 hours, while in other situations 10 minutes would make more sense.