using the volumes from Site B. After the failover operation processes, the volumes
at Site B are available to be mounted and used by a host. You can use the volumes
from Site B to restart your application.
The failback operation resynchronizes the volumes in the following manner
depending on the volume state:
v If a volume at Site A is in simplex state, all of the data for that volume is sent
from Site B to Site A.
v If a volume at Site A is in full-duplex or suspended state and without changed
tracks, only the modified data on the volume at Site B is sent to the volume at
Site A.
v If a volume at Site A is in a suspended state but has tracks that have been
modified, the volume at Site B will discover which tracks were modified at any
site and send both tracks that were changed on Site A and the tracks marked at
Site B from Site A to Site B.
The following assumptions are made for this scenario:
v Paths from Site B to Site A are created.
v Remote mirror and copy volume pairs are created. Site B volume is the source
volume of the failback operation. This volume was initially the target volume of
the relationship.
Perform
the following steps using the DS Storage Manager. You can also use the
DS CLI to perform Copy Services functions.
Note: For details on individuals tasks, see the related topics section.
1. Perform a failback operation at Site B. As a result, data that has been modified
at Site B for the specified volumes will be sent from Site B to Site A. Data that
was modified at Site A after the switch to Site B will be overwritten by the data
from Site B.
2. Before returning to normal operation, quiesce your application (still updating
volumes at Site B) to cease all write I/O from updating the source volumes.
Depending on the host operating system, it might be necessary to unmount the
source volumes.
3. Perform another failover recovery operation at Site A. This process converts the
full-duplex target volumes at the Site A to suspended source volumes. The
volumes at Site A start the change recording process while in failover mode.
4. Depending on your operating system, it might be necessary to rescan Fibre
Channel devices and mount the new source volumes at Site A.
5. After the failover operation completes, you can restart the applications in normal
production at Site A and check for consistency. When your applications are
started, all write I/O to the new source volumes will be tracked by the bitmap
that is created.
6. From Site A, create paths in the opposite direction from Site A to Site B.
7. From Site A, perform another failover and failback operation using the source
volumes. This process resynchronizes the volumes between your Sites A and B.
Start your applications at Site A and check for consistency.
8. Mount your volumes at Site A and start your applications on your primary server.
144 DS8000 User’s Guide
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