Tuning VxVM

VERITAS Volume Manager (VxVM) is tuned for most configurations ranging from small systems to larger servers. On smaller systems with less than a hundred drives, tuning should not be necessary and VERITAS Volume Manager should be capable of adopting reasonable defaults for all configuration parameters. On very large systems, however, there may be configurations that require additional tuning of these parameters, both for capacity and performance reasons. For information on tuning VERITAS Volume Manager, refer to the "Tuning VxVM" section of the "Performance Monitoring and Tuning" chapter in the VERITAS Volume Manager Administrator's Guide.

Obtaining Volume I/O Statistics

If your database is created on a single file system that is on a single volume, there is typically no need to monitor the volume I/O statistics. If your database is created on multiple file systems on multiple volumes, or the volume configurations have changed over time, it may be necessary to monitor the volume I/O statistics for the databases.

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. Use the -g option to specify the database disk group to report statistics for objects in that database disk group.

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)

VxVM records the preceding three pieces of information for logical I/Os, including reads, writes, atomic copies, verified reads, verified writes, plex reads, and plex writes for each volume. VxVM also maintains other statistical data such as read failures, write failures, corrected read failures, corrected write failures, and so on. In addition to displaying volume statistics, the vxstat command is capable of displaying more detailed statistics on the components that form the volume. For detailed information on available options, refer to the vxstat(1M) manual page.

To reset the statistics information to zero, use the -r option. You can reset the statistics information 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:

The "Performance Monitoring" section of the "Performance Monitoring and Tuning" chapter in the VERITAS Volume Manager Administrator's Guide provides detailed information on how to use the vxstat output to identify volumes that have excessive activity and how to reorganize, change to a different layout, or move these volumes.

Additional volume statistics are available for RAID-5 configurations. Refer to the vxstat(1M) manual page for more information.