NFS option tunable parameters

Most of the NFS option tunable parameters are fully described in the nfso man page. The following are a few other related parameters:

1. combehind

   Item	Descriptor
   Purpose:	Enables commit-behind behavior on the NFS client when writing very large files over NFS Version 3 mounts.
   Values:	Default: 0; Range: 0 to 1
   Display:	mount
   Change:	mount -o combehind
   Diagnosis:	Poor throughput when writing very large files (primarily files larger than the amount of system memory in the NFS client) over NFS Version 3 mounts.
   Tuning:	Use this mount option on the NFS client if the primary use of NFS is to write very large files to the NFS server. Note that an undesirable feature of this option is that VMM caching of NFS file data is effectively disabled on the client. Therefore, use of this option is discouraged in environments where good NFS read performance is necessary.

2. nfsd Count

   Item	Descriptor
   Purpose:	Specifies the maximum number of NFS server threads that are created to service incoming NFS requests.
   Values:	Default: 3891; Range: 1 to 3891
   Display:	ps -efa | grep nfsd
   Change:	chnfs -n NewValue Change takes effect immediately and is permanent. The -N flag causes an immediate, temporary change. The -I flag causes a change that takes effect at the next boot.
   Diagnosis:	See nfs_max_threads
   Tuning:	See nfs_max_threads
   Refer to:	Number of necessary biod threads

3. numclust

   Item	Descriptor
   Purpose:	Used in conjunction with the combehind option to improve write throughput performance when writing large files over NFS Version 3 mounts.
   Values:	Default: 128; Range: 8 to 1024
   Display:	mount
   Change:	mount -o numclust=NewValue
   Diagnosis:	Poor throughput when writing very large files (primarily files larger than the amount of system memory in the NFS client) over NFS Version 3 mounts.
   Tuning:	Use this mount option on the NFS client if the primary use of NFS is to write very large files to the NFS server. The value basically represents the minimum number of pages for which VMM will attempt to generate a commit operation from the NFS client. Too low a value can result in poor throughput due to an excessive number of commits (each of which results in synchronous writes on the server). Too high a value can also result in poor throughput due to the NFS client memory filling up with modified pages which can cause the LRU daemon to be invoked to start reclaiming pages. When the lrud runs, V3 writes essentially become synchronous because each write ends up being accompanied by a commit. This situation can be avoided by using the numclust and combehind options.