Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 15, Performance Monitoring and Tuning
Performance Monitoring
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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.
Tracing Volume Operations
Use the vxtrace command to trace operations on specified volumes, kernel I/O object
types or devices. The vxtrace command either prints kernel I/O errors or I/O trace
records to the standard output or writes the records to a file in binary format. Binary trace
records written to a file can also be read back and formatted by vxtrace.