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485Performance 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.