Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

463Performance monitoring and tuning
Tuning VxVM
3 Display level 1 and 2 messages plus messages that relate to I/O errors, I/O error
analysis and path media errors.
4 Display level 1, 2 and 3 messages plus messages that relate to setting or
changing attributes on a path.
dmp_path_age
The time for which an intermittently failing path needs to be monitored as healthy before
DMP once again attempts to schedule I/O requests on it. The default value is 300 seconds.
The minimum value is 1 second. The value of this tunable may be changed by using the
vxdmpadm settune command.
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 for an array as described in “Specifying the I/O policy” on
page 141.
The value of this tunable may be changed by using the
vxdmpadm settune command.
dmp_probe_idle_lun
If DMP statistics gathering is enabled, set to 1 (default) to have the DMP path restoration
thread probe idle LUNs, or to 0 to turn off this feature. (Idle LUNs are VM disks on which
no I/O requests are scheduled.) The value of this tunable is only interpreted when DMP
statistics gathering is enabled. Turning off statistics gathering also disables idle LUN
probing. The value of this tunable may be changed by using the
vxdmpadm settune
command.
dmp_queue_depth
The maximum number of queued I/O requests on a path during I/O throttling. The default
value is 20. The value of this tunable may be changed by using the
vxdmpadm settune