VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Performance Monitoring and Tuning
Performance Monitoring
Chapter 12 391
Performance Monitoring
As a system administrator, you have two sets of priorities for setting
priorities for performance. One set is physical, concerned with hardware
such as disks and controllers. The other set is logical, concerned with
managing software and its operation.
Setting Performance Priorities
The important physical performance characteristics of disk hardware are
the relative amounts of I/O on each drive, and the concentration of the
I/O within a drive to minimize seek time. Based on monitored results,
you can then move the location of subdisks to balance I/O activity across
the disks.
The logical priorities involve software operations and how they are
managed. Based on monitoring, you may choose to change the layout of
certain volumes to improve their performance. You might even choose to
reduce overall throughput to improve the performance of certain critical
volumes. Only you can decide what is important on your system and
what trade-offs you need to make.
Best performance is usually achieved by striping and mirroring all
volumes across a reasonable number of disks and mirroring between
controllers, when possible. This procedure tends to even out the load
between all disks, but it can make VxVM more difficult to administer.
For large numbers of disks (hundreds or thousands), set up disk groups
containing 10 disks, where each group is used to create a striped-mirror
volume. This technique provides good performance while easing the task
of administration.
Obtaining Performance Data
VxVM provides two types of performance information: I/O statistics and
I/O traces. Each of these can help in performance monitoring. You can
obtain I/O statistics using the vxstat command, and I/O traces using the
vxtrace command. A brief discussion of each of these utilities may be
found in the following sections.