VERITAS Volume Manager 4.1 Administrator's Guide

Performance Monitoring and Tuning
Tuning VxVM
Chapter 12406
Tuning VxVM
This section describes how to adjust the tunable parameters that control
the system resources 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. In cases where tuning can be used 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. Any tuning changes must be performed with
care, as they may adversely affect overall system performance or may
even leave VxVM unusable.
Tuning Guidelines for Large Systems
On smaller systems (with less than a hundred disk drives), tuning is
unnecessary and VxVM is capable of adopting 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 (1M)command to select from, and also allow for the
creation of larger arrays. 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 with the result 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. This involves re-initializing each disk in the disk group (and
can involve reconfiguring everything and restoring from backup).