Dynamic Multi-Pathing (DMP) maintains a kernel task that re-examines the condition of paths at a specified interval. The type of analysis that is performed on the paths depends on the checking policy that is configured.
When configuring DMP path restoration policies, you must stop the path restoration thread, and then restart it with new attributes.
Use the vxdmpadm settune dmp_restore_policy command to configure one of the following restore policies. The policy remains in effect until the restore thread is stopped or the values are changed using the vxdmpadm settune command.
# vxdmpadm settune dmp_restore_policy=check_all
The path restoration thread checks that at least one alternate path is healthy. It generates a notification if this condition is not met. This policy avoids inquiry commands on all healthy paths, and is less costly than check_all in cases where a large number of paths are available. This policy is the same as check_all if there are only two paths per DMP node. The command to configure this policy is:
# vxdmpadm settune dmp_restore_policy=check_alternate
This is the default path restoration policy. The path restoration thread checks the condition of paths that were previously disabled due to hardware failures, and revives them if they are back online. The command to configure this policy is:
# vxdmpadm settune dmp_restore_policy=check_disabled
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 a large number of paths are available. The command to configure this policy is:
# vxdmpadm settune dmp_restore_policy=check_periodic
The default number of cycles between running the check_all policy is 10.
The dmp_restore_interval tunable parameter specifies how often the path restoration thread examines the paths. For example, the following command sets the polling interval to 400 seconds:
# vxdmpadm settune dmp_restore_interval=400
The settings are immediately applied and are persistent across reboots. Use the vxdmpadm gettune command to view the current settings.
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.