VERITAS Volume Manager 4.1 Administrator's Guide

Performance Monitoring and Tuning
Performance Monitoring
Chapter 12 401
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.
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: