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

Performance Monitoring and Tuning
Performance Monitoring
Chapter 12392
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.
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.
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.