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

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. For I/O related to reclaim operations, the I/O trace records indicate that
it is a reclaim I/O. Binary trace records written to a file can also be read back and
formatted by vxtrace.
If you do not specify any operands, vxtrace reports either all error trace data or
all I/O trace data on all virtual disk devices. With error trace data, you can select
all accumulated error trace data, wait for new error trace data, or both of these
(this is the default action). Selection can be limited to a specific disk group, to
specific VxVM kernel I/O object types, or to particular named objects or devices.
See the vxtrace(1M) manual page.
Printing volume statistics
Use the vxstat command to access information about activity on volumes, plexes,
subdisks, and disks under VxVM control, and to print summary statistics to the
standard output. These statistics represent VxVM activity from the time the
system initially booted or from the last time the counters were reset to zero. If no
VxVM object name is specified, statistics from all volumes in the configuration
database are reported.
VxVM records the following I/O statistics:
■ count of operations
■ number of blocks transferred (one operation can involve more than one block)
489Performance monitoring and tuning
Performance monitoring