Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

456 Performance monitoring and tuning
Performance monitoring
For detailed information about how to use vxtrace, refer to 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)
■ average operation time (which reflects the total time through the VxVM interface and
is not suitable for comparison against other statistics programs)
These statistics are recorded for logical I/O including reads, writes, atomic copies, verified
reads, verified writes, plex reads, and plex writes for each volume. As a result, one write to
a two-plex volume results in at least five operations: one for each plex, one for each
subdisk, and one for the volume. Also, one read that spans two subdisks shows at least
four reads—one read for each subdisk, one for the plex, and one for the volume.
VxVM also maintains other statistical data. For each plex, it records read and write
failures. For volumes, it records corrected read and write failures in addition to read and
write failures.
To reset the statistics information to zero, use the
-r option. This can be done for all
objects or for only those objects that are specified. Resetting just prior to an operation
makes it possible to measure the impact of that particular operation.
The following is an example of output produced using the vxstat command:
OPERATIONS BLOCKS AVG TIME(ms)
TYP NAME READ WRITE READ WRITE READ WRITE
vol blop 0 0 0 0 0.0 0.0
vol foobarvol 0 0 0 0 0.0 0.0
vol rootvol 73017 181735 718528 1114227 26.8 27.9
vol swapvol 13197 20252 105569 162009 25.8 397.0
vol testvol 0 0 0 0 0.0 0.0
Additional volume statistics are available for RAID-5 configurations.
For detailed information about how to use
vxstat, refer to the vxstat(1M) manual page.
Using performance data
When you have gathered performance data, you can use it to determine how to configure
your system to use resources most effectively. The following sections provide an
overview of how you can use this data.