Managing NFS and KRPC Kernel Configurations in HP-UX 11i v2 (Oct 2008)

to continue issuing NFS READ calls even when all the biods are busy servicing asynchronous write
requests. In many situations this may improve application performance. In some situations with
NFSv2 mounts, NFS read performance may regress by enabling this tunable. If application
performance is negatively affected with this tunable enabled, set the tunable back to the default value
(disabled).
Tested Values
Default: 0 (Tunable is disabled)
Min: 0
Max: 1 (Tunable is enabled)
Restrictions on Changing
The nfs_async_read_avoidance_enabled tunable is dynamic. System reboot is not required to activate
a change made to this tunable. Changes made to the nfs_async_read_avoidance tunable are
applicable to all NFS mounted filesystems.
Modifying the Value
If an application experiences poor read performance on an NFS filesystem, enabling the
nfs_async_read_avoidance_enabled tunable can improve the read performance. This tunable is not
available in the next release of HP-UX. Starting with the HP-UX 11i v3 release, this feature is enabled
by default and is not user-configurable.
2.1.2 nfs_clnt_avoid_write_copy
Description
When servicing write requests, the NFS client will make separate copies of the write data in kernel
memory multiple times as part of processing each request. HP recently identified one of these in-
memory copies as being unnecessary, and by eliminating this additional copy the performance of
sending write requests increases. The nfs_clnt_avoid_write_copy tunable controls whether the NFS
client will avoid this unnecessary in-memory copy or continue using the standard write logic.
Tested Values
Default: 0 (Tunable is disabled)
Min: 0
Max: 1 (Tunable is enabled)
Restrictions on Changing
The nfs_clnt_avoid_write_copy tunable is dynamic. System reboot is not required to activate a change
made to this tunable. Changes made to the nfs_clnt_avoid_write_copy tunable are applicable to all
NFS mounted filesystems.
Modifying the Value
Enable this tunable to improve the write performance of NFS. This tunable is not supported in the
HP-UX 11i v3 release. HP is evaluating the possibility of adding support for this feature in a future 11i
v3 ONCplus ISU release.
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