Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

470 Performance monitoring and tuning
Tuning VxVM
Note: The memory allocated for this cache is exclusively dedicated to it. It is not available
for other processes or applications.
Setting the value of volpagemod_max_memsz below 512KB fails if cache objects or
volumes that have been prepared for instant snapshot operations are present on the system.
If you do not use the FastResync or DRL features that are implemented using a version 20
DCO volume, the value of volpagemod_max_memsz can be set to 0. However, if you
subsequently decide to enable these features, you can use the
vxtune command to change
the value to a more appropriate one:
# vxtune volpagemod_max_memsz value
where the new value is specified in kilobytes. Using the
vxtune command to adjust the
value of volpagemod_max_memsz does not persist across system reboots unless you
also adjust the value that is configured in the /stand/system file.
volraid_minpool_sz
The initial amount of memory that is requested from the system by VxVM for RAID-5
operations. The maximum size of this memory pool is limited by the value of
voliomem_maxpool_sz.
The default value for this tunable is 16348 sectors (16MB).
volraid_rsrtransmax
The maximum number of transient reconstruct operations that can be performed in parallel
for RAID-5. A transient reconstruct operation is one that occurs on a non-degraded RAID-
5 volume that has not been predicted. Limiting the number of these operations that can
occur simultaneously removes the possibility of flooding the system with many
reconstruct operations, and so reduces the risk of causing memory starvation.
The default number of transient reconstruct operations that can be performed in parallel is
1.
Increasing this size improves the initial performance on the system when a failure first
occurs and before a detach of a failing object is performed, but can lead to memory
starvation.