NFS Performance Tuning for HP-UX 11.0 and 11i Systems
nfs performance tuning for hp-ux 11.0 and 11i systems page 37
Notes:
Page 37July 22, 2002
Copyright 2002 Hewlett- Packard Company
Why else would you consider
disabling biods on your NFS client?
• Avoid blocking access to all servers when one is down
Ø All biods can block on a dead server and hang access to any working servers
• Applications performing mainly non-sequential reads
Ø Read-ahead data will likely be ignored – wasted overhead
• Applications performing primarily synchronous I/O
Ø Biods are disabled for synchronous I/O requests
• Relax 25% buffer cache limitation for asynchronous I/O
Ø This buffer cache limitation is disabled when biods are not running
• Client application locks the NFS file being written to
Ø Kernel disables buffer cache for the locked file – forcing synchronous behavior
biod
Avoid blocking access to all servers when one is down
If one NFS server stops responding while biods are running, all biods can potentially hang
waiting for that server to respond, effectively stopping all NFS I/O – even to available servers.
If no biods are running then client processes would still be able to access any available servers.
Applications performing mainly non-sequential reads
If the client applications are performing primarily non-sequential reads, any data pre-fetched by
the biods will likely be unwanted by the applications, resulting in wasted overhead from
unnecessary read-aheads.
Applications performing primarily synchronous I/O
When an application opens a file with the O_SYNC, O_DSYNC, or O_RSYNC flags, the kernel
effectively disables the use of biods for any reads and writes to the file.
Relax 25% buffer cache limitation for asynchronous I/O
The NFS client is allowed to use a maximum of 25% of buffer cache memory for staging
asynchronous write data. This 25% limit is only enforced when b iods are running.
Client application locks the NFS file being written to
When an application locks an NFS-mounted file, any read or write requests made to this file
will be performed synchronously. In effect, buffer cache and biods are disabled for that file
when a lock is present, so no benefit is gained by running biod daemons in this case.