When the system contains multiple paths to an LU and an error occurs on the path that is currently being used, HDLM can switch to another functional path, so that the system can continue operating. This is called a failover.
If a path in which an error has occurred recovers from the error, HDLM can then switch back to that path. This is called a failback.
Two types of failovers and failbacks are available:
Automatic failovers and failbacks
Manual failovers and failbacks
Failovers and failbacks switch which path is being used and also change the statuses of the paths. A path status is either online or offline. An online status means that the path can receive I/Os. On the other hand, an offline status means that the path cannot receive I/Os. A path will go into the offline status for the following reasons:
An error occurred on the path.
A user executed the HDLM command's offline operation.
For details on the offline operation, see offline (places paths offline).
For details on path statuses and the transitions of those statuses, see Path status transition.