HP StorageWorks P4000 User Manual page 45

Data availability if the primary volume or production application server fails
If either the primary volume or production application server in your production site fails, only that
data written to the volume since the last remote snapshot was created is unavailable until the volume
or production application server is restored.
Failover to the backup application server
To maintain availability of the applications and the remaining data, the following process occurs:
1. A script or other application monitoring the production application server discovers that the
primary volume is not available. A script executes to fail over to the backup application server.
2. The backup application server executes a script to convert the remote volume into a primary
volume so that the volume can be accessed by the backup application server. For information
about scripting, see the CLIQ The SAN/iQ Command-Line Interface User Manual and the
sample scripts available at http://www.hp.com/go/P4000downloads.
3. Because the backup application server was configured to access the remote (now primary) volume,
operation of the backup application server begins.
The application continues to operate after the failover to the backup application server.
Failback to the production configuration
When the production server and volumes become available again, you have the following two failback
options:
Resume operations using the original production server, and then return the backup volumes to
their original remote status, as illustrated in
that was written to the backup volumes since the failure back onto the production volumes.
Continue operating on the backup application server. When the production server and volumes
become available, configure the production server to be the backup server (role reversal).
Merging data for failback
In the failover scenarios described above, there are probably two snapshots with different data. As
part of failback, users must make a decision whether to merge the data from the two snapshots and
the most effective method for doing so. For more information see
the acting primary volume and the original primary
Figure 12 on page 46. This requires migration of data
"Synchronizing the data between
volume" on page 37.
P4000 Remote Copy user guide 45