ONCplus B.11.31.13 Release Notes (5900-1979, March 2012)

3 Known Problems and Workarounds

This section lists known problems, probable causes, and appropriate workarounds.

Problem

There is a possibility for an HP-UX 11i v3 system to experience a system hang under the following

conditions:

• An application writes a huge NFS file to a filesystem using NFS loopback mount.

• Two systems NFS-mount file systems from each other and simultaneously write huge amounts

of data to each other.

Causes

On an HP-UX 11i v3 system with NFS loopback mount enabled, there is a possibility for an

application to consume the entire file cache memory while writing a huge NFS file. This could lead

to a deadlock between the NFS client and NFS server modules.

For example, when the NFS client consumes the entire file cache, the server cannot execute any

of the WRITE requests sent by the client because of the non-availability of file cache memory. This

can result in non-availability of file cache memory for other mounted file systems on the node.

There is a high possibility for this problem to occur if the system is configured with low file cache

memory.

For example, when the filecache_min and filecache_max parameters are configured in the range

of 1% to 5% of the total physical memory.

Workaround

Starting from ONCplus B.11.31.13 onwards, a fix has been implemented for this issue.

Two new tunables, namely, kctune nfs_enable_ufc_threshold and kctune

nfs3_ufc_threshold_percentage have been introduced. To avoid this issue, the tunables must be

set to the following values:

• kctune nfs_enable_write_behind = 1

• kctune nfs_enable_ufc_threshold = 1

• kctune nfs3_ufc_threshold_percentage = 50

For more information about the new tunables, see the Managing NFS and KRPC Kernel

Configurations in HP-UX 11i v3 whitepaper.

For ONCplus B.11.31.12 and earlier versions, the workaround is to use the "forcedirectio"

option for the NFS mount.

NOTE: This solution is implemented for NFS v3 only as of now. All NFS v3 filesystems have to

be unmounted if there is any change in these tunables or UFC filecache_max.

Problem

When ONCplus B.11.31.12 is operating in the SRP environment, if the srp -stop command is

executed while there are active NFS mount points present in the SRP environment, it may hang

and a message similar to the following will be logged in the /var/adm/syslog/syslog.log

file:

vmunix: WARNING: SRP 13 shutdown called with 1 active NFS mounts. Waiting

for unmount to complete.