VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Performance Monitoring
Chapter 9 397
reports statistics that reflect the activity levels of Volume Manager
objects since boot time. Statistics for a specific Volume Manager object, or
all objects, can be displayed at one time. A disk group can also be
specified, in which case statistics for objects in that disk group only are
displayed. If no disk group is specified, rootdg is assumed.
The amount of information displayed depends on what options are
specified to the vxstat utility. For detailed information on available
options, see the vxstat(1M) manual page.
Volume Manager records the following I/O statistics:
• a count of operations
• the number of blocks transferred (one operation can involve more
than one block)
• the average operation time (which reflects the total time through the
Volume Manager interface and is not suitable for comparison against
other statistics programs)
Volume Manager records the preceding I/O statistics for logical I/Os. The
statistics include 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.
Volume Manager also maintains other statistical data. For each plex,
read failures and write failures are maintained. For volumes, corrected
read failures and write failures accompany the read failures and write
failures.
The vxstat utility can also reset the statistics information to zero. Use
the vxstat -r command to clear all statistics. 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 utility:
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