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.
The DMP path restoration thread does not change the disabled state of the path through a controller that you have disabled using
restore command to configure one of the following policies:
vxdmpadm start 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 start 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 start 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 there is a large number of paths available. The command to configure this policy is:
vxdmpadm start restore policy=check_periodic \
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
To change the interval or policy, first stop the path restoration thread, and then restart it with new attributes.
See "Stopping the DMP path restoration thread" on page 148.