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

Chapter 15, Performance Monitoring and Tuning
Tuning VxVM
411
Tunable Parameters
The following sections describe specific tunable parameters.
dmp_enable_restore_daemon
Set to 1 to enable the DMP restore daemon; set to 0 to disable.
dmp_failed_io_threshold
The time limit for an I/O request in DMP. If the time exceeds this value, the usual result is
to mark the disk as bad.
dmp_pathswitch_blks_shift
The default number of contiguous I/O blocks (expressed as the integer exponent of a
power of 2; for example 10 represents 1024 blocks) that are sent along a DMP path to an
Active/Active array before switching to the next available path.
The default value of this parameter is set to 10 so that 1024 blocks (1MB) of contiguous
I/O are sent over a DMP path before switching. For intelligent disk arrays with internal
data caches, better throughput may be obtained by increasing the value of this tunable.
For example, for the HDS 9960 A/A array, the optimal value is between 14 and 16 for an
I/O activity pattern that consists mostly of sequential reads or writes.
Note This parameter only affects the behavior of the balanced I/O policy. A value of 0
disables multipathing for the policy unless the vxdmpadm command is used to
specify a different partition size as described in “Specifying the I/O Policy” on
page 121.
dmp_restore_daemon_cycles
If the DMP restore policy is CHECK_PERIODIC, the number of cycles after which the
CHECK_ALL policy is called.
dmp_restore_daemon_interval
The time in seconds between two invocations of the DMP Restore Daemon.