Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Tuning VxVM
This section describes how to adjust the tunable parameters that control the
system resources that are used by VxVM. Depending on the system resources that
are available, adjustments may be required to the values of some tunable
parameters to optimize performance.
General tuning guidelines
VxVM is optimally tuned for most configurations ranging from small systems to
larger servers. When you can use tuning to increase performance on larger systems
at the expense of a valuable resource (such as memory), VxVM is generally tuned
to run on the smallest supported configuration. You must perform any tuning
changes with care. Changes may adversely affect overall system performance or
may even leave VxVM unusable.
Various mechanisms exist for tuning VxVM. You can tune many parameters using
the System Management Homepage (SMH) or the kctune utility. Other values can
only be tuned using the command line interface to VxVM.
See “Changing the values of VxVM tunables” on page 495.
Tuning guidelines for large systems
On smaller systems (with fewer than a hundred disk drives), tuning is unnecessary.
VxVM can adopt reasonable defaults for all configuration parameters. On larger
systems, configurations can require additional control over the tuning of these
parameters, both for capacity and performance reasons.
Generally, only a few significant decisions must be made when setting up VxVM
on a large system. One is to decide on the size of the disk groups and the number
of configuration copies to maintain for each disk group. Another is to choose the
size of the private region for all the disks in a disk group.
Larger disk groups have the advantage of providing a larger free-space pool for
the vxassist command to select from. They also allow for the creation of larger
volumes. Smaller disk groups do not require as large a configuration database
and so can exist with smaller private regions. Very large disk groups can eventually
exhaust the private region size in the disk group. The result is that no more
configuration objects can be added to that disk group. At that point, the
configuration either has to be split into multiple disk groups, or the private regions
have to be enlarged. Each disk in the disk group must be re-initialized. This can
involve reconfiguring everything and restoring from backup.
Performance monitoring and tuning
Tuning VxVM
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