DMP maintains a kernel thread 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.
Note: |
The DMP path restoration thread does not change the disabled state of the path through a controller that you have disabled using vxdmpadm disable. |
When configuring DMP path restoration policies, you must stop the path restoration thread, and then restart it with new attributes.
Use the vxdmpadm start restore command to configure one of the following restore policies. The policy will remain in effect until the restore thread is stopped or the values are changed using vxdmpadm settune command.
The path restoration thread analyzes all paths in the system and revives the paths that are back online, as well as disabling the paths that are inaccessible. The command to configure this policy is:
# vxdmpadm start restore [interval=seconds] 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 start restore [interval=seconds] \ 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 start restore [interval=seconds] \ 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 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.
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.