Hp XP7 Storage Manuel d'utilisateur télécharger pdf (Page 37)

Performing Failovers and Failbacks Using Path Switching

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 intentionally placed the path offline by using the Path Management

window in the HDLM GUI.

• A user executed the HDLM command's offline operation.

For details on the offline operation, see

offline (Places Paths Offline) on

page 6-6.

• Hardware, such as cables or HBAs, has been removed.

For details on path statuses and the transitions of those statuses, see

Path

Status Transition on page 2-20.

Automatic Path Switching

The following describes the automatic failover and failback functions, which

automatically switch a path.

Automatic Failovers

If you detect an error on the path that is currently being used, you can

continue to use the system by having the status of that path automatically

changed to offline, and then automatically have the system switch over to

another online path. This functionality is called automatic failover. Automatic

failovers can be used for the following levels of errors:

Critical

A fatal error that might stop the system.

Error

A high-risk error, which can be avoided by performing a failover or some

other countermeasure.

For details on error levels, see Filtering of Error Information on page 2-36.

HDLM Functions

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Hp XP7 Storage Manuel d'utilisateur Page 37

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