Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

152 Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
Configuring DMP path restoration policies
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.
Use the
start restore command to configure one of the following policies:
■ check_all
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 policy=check_all [interval=seconds]
■ check_alternate
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 \
[interval=seconds]
■ check_disabled
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 \
[interval=seconds]
■ 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 policy=check_periodic \
interval=seconds [period=number]
The interval attribute must be specified for this policy. The default number of
cycles between running the check_all policy is 10.