ONCplus B.11.31.14 Release Notes (5900-2268, April 2012)

3 Known Problems and Workarounds
This section lists known problems, probable causes, and appropriate workarounds.
Problem
On an HP-UX 11i v3 system running ONCplus B.11.31.13, when the “nfs_enable_ufc_threshold”
tunable is enabled, the following issues may occur:
• The write operation may be interrupted when very large files are copied over NFS.
• System crash may occur under heavy load conditions.
Solution
This problem has been fixed in ONCplus B.11.31.14.
Workaround
For ONCplus B.11.31.13, the workaround is to use the forcedirectio option for the NFS
mount in case of loopback mount or cross mounts with very less UFC cache (say 1%) configured
on NFS client systems.
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.
Solution
Starting from ONCplus B.11.31.14 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
18 Known Problems and Workarounds