Moving production to Site B after unplanned outages (failover)
In this situation, you have lost access to your production site, Site A. You can switch
production to your recovery site (Site B) allowing the processing of data to resume
at Site B. This process is known as a failover recovery.
In a disaster recovery environment, when two storage units are set up in two
geographically distinct locations, we refer to the storage unit at the production or
local site as Site A and the storage unit at the remote or recovery site as Site B.
For this scenario, assume that an unexpected failure occurs at Site A, making it
unavailable. Production must be moved to Site B.
The failover operation is issued to the storage unit that will become the primary.
That is, production will failover to Site B during this outage, which will make the
target volumes at Site B convert to source volumes and cause them to suspend.
Your original source volumes at Site A remain in the state they were in at the time
of the site switch. When Site A is available again, application I/O is switched back
from Site B to Site A. See Table 4 for an example of the implementation of failover
and failback operations.
Perform the following steps using the DS Storage Manager. You can also use the
DS CLI to perform Copy Services functions.
1. Perform a failover recovery operation to Site B. After the failover operation has
processed successfully, the volumes at Site B transition from target to source
volumes.
2. Mount your target volumes on your server at Site B.
3. Start your applications on your server at Site B.
4. After Site A recovers, proceed with the following steps, which are the first taken
to recover the volumes at Site A.
a. Create paths between LSSs at Site B to Site A to allow the volumes at Site
A to be synchronized with the Site B volumes.
b. Delete any remote mirror and copy volume relationships that still exist from
the source volumes.
c. Wait until the volumes are in full duplex state, then schedule a time to
perform a failback recovery operation using the volumes at Site A. This
process resynchronizes the volumes at Site A with the volumes at Site B.
Note: Failback recovery operations are usually used after a failover
recovery has been issued to restart mirroring either in the reverse
direction (remote site to local site) or original direction (local site to
remote site).
Table 4. Failover and failback implementation
Step Operation
Manage-
ment
required
to
Format of
source volume
and target
volume
Format of
source and
target volume
pair Result: Site A Result: Site B
1
Chapter 10. Disaster recovery using Copy Services 145
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