VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Tuning the Volume Manager
Chapter 9408
voliomem_maxpool_sz
This tunable defines the maximum memory used by a Volume Manager
from the system for its internal purposes. The default value of this
tunable is 4 Megabytes. This tunable has a direct impact on the
performance of VxVM.
voliomem_chunk_size
System memory is allocated to and released from the Volume Manager
using this granularity. A larger granularity reduces memory allocation
overhead (somewhat) by allowing Volume Manager to keep hold of a
larger amount of memory.
The default size for this tunable is 64K.
Tuning for Large Systems
On smaller systems (less than a hundred drives), tuning should be
unnecessary and the Volume Manager should be capable of adopting
reasonable defaults for all configuration parameters. On larger systems,
however, there may be configurations that require additional control over
the tuning of these parameters, both for capacity and performance
reasons.
Generally, there are only a few significant decisions to be made when
setting up the Volume Manager 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, however, require as
large a configuration database and so can exist with smaller private
regions.Very large disk groups caneventually 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).
A general recommendation for users ofdisk array subsystems isto create
a single disk group for each array so the disk group can be physically
moved as a unit between systems.