Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

■ check_periodic
The path restoration thread performs check_all once in a given number of
cycles, and check_disabled in the remainder of the cycles. This policy may
lead to periodic slowing down (due to check_all) if there is a large number of
paths available. The command to configure this policy is:
# vxdmpadm start restore interval=seconds \
policy=check_periodic [period=number]
The interval attribute must be specified for this policy. The default number
of cycles between running the check_all policy is 10.
The interval attribute specifies how often the path restoration thread examines
the paths. For example, after stopping the path restoration thread, the polling
interval can be set to 400 seconds using the following command:
# vxdmpadm start restore interval=400
Starting with the 5.0MP3 release, you can also use the vxdmpadm settune command
to change the restore policy, restore interval, and restore period. This method
stores the values for these arguments as DMP tunables. The settings are
immediately applied and are persistent across reboots. Use the vxdmpadm gettune
to view the current settings.
See “DMP tunable parameters” on page 504.
If the vxdmpadm start restore command is given without specifying a policy or
interval, the path restoration thread is started with the persistent policy and
interval settings previously set by the administrator with the vxdmpadm settune
command. If the administrator has not set a policy or interval, the system defaults
are used. The system default restore policy is check_disabled. The system default
interval is 300 seconds.
Warning: Decreasing the interval below the system default can adversely affect
system performance.
Stopping the DMP path restoration thread
Use the following command to stop the DMP path restoration thread:
# vxdmpadm stop restore
Warning: Automatic path failback stops if the path restoration thread is stopped.
195Administering Dynamic Multi-Pathing
Administering DMP using vxdmpadm