Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Tuning VxVM
408 VERITAS Volume Manager Administrator’s Guide
controllers can be used, and the speed of the system bus. If a particularly busy volume has
a high ratio of reads to writes, it is likely that mirroring can significantly improve
performance of that volume.
Using I/O Tracing
I/O statistics provide the data for basic performance analysis; I/O traces serve for more
detailed analysis. With an I/O trace, focus is narrowed to obtain an event trace for a
specific workload. This helps to explicitly identify the location and size of a hot spot, as
well as which application is causing it.
Using data from I/O traces, real work loads on disks can be simulated and the results
traced. By using these statistics, you can anticipate system limitations and plan for
additional resources.
For information on using the vxdmpadm command to gather I/O statistics for a DMP
node, path, or enclosure, see “Gathering and Displaying I/O Statistics” on page 117. You
can also use the vxdmpadm command to change the I/O load-balancing policy for an
enclosure as described in “Specifying the I/O Policy” on page 121.
Tuning VxVM
This section describes how to adjust the tunable parameters that control the system
resources used by VxVM. Depending on the system resources that are available,
adjustments may be required to the values of some tunable parameters to optimize
performance.
General Tuning Guidelines
VxVM is optimally tuned for most configurations ranging from small systems to larger
servers. In cases where tuning can be used to increase performance on larger systems at
the expense of a valuable resource (such as memory), VxVM is generally tuned to run on
the smallest supported configuration. Any tuning changes must be performed with care,
as they may adversely affect overall system performance or may even leave VxVM
unusable.
Various mechanisms exist for tuning VxVM. Many parameters can be tuned using the
System Administration Manager (SAM) or the kctune utility. Other values can only be
tuned using the command line interface to VxVM.