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477Performance monitoring and tuning
Tuning VxVM
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 147.
The value of this tunable is changed by using the
vxdmpadm settune command.
dmp_probe_idle_lun
If DMP statistics gathering is enabled, set to on (default) to have the DMP path
restoration thread probe idle LUNs, or to
off 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 is 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 40.
The value of this tunable is changed by using the vxdmpadm settune command.
See “Configuring the I/O throttling mechanism” on page 157.
dmp_restore_cycles
If the DMP restore policy is CHECK_PERIODIC, the number of cycles after which
the CHECK_ALL policy is called.
The value of this tunable is only changeable by using the vxdmpadm start
restore
command.
dmp_restore_interval
The time in seconds between two invocations of the DMP path restoration
thread.
The value of this tunable is only changeable by using the vxdmpadm start
restore
command.