HP Veritas Volume Manager 5.0 -UX 11i v3 manual Tuning VxVM, General tuning guidelines

472Performance monitoring and tuning

Tuning VxVM

writes where mirroring can improve performance depends greatly on the disks, the disk controller, whether multiple 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 144. 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 147.

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 Management Homepage (SMH) or the kctune utility. Other values can only be tuned using the command line interface to VxVM.