Use this process to perform failover and restore operations at
your remote site during an unplanned outage, using E volumes at the
intermediate site.
If possible, before you issue a failover operation to the remote
site, ensure that data processing has completely stopped at the local
and intermediate sites and issue a freeze to the A volumes at the
local site. If you fail to do so and data is copied to the A and B
volume pairs at the local and intermediate sites, a failover to the
remote site can cause a data loss.
For this scenario, assume that host I/O processing is being sent
to the local site in a Metro/Global Mirror configuration. A failure
occurs at Site A and it is not possible to run your systems using
the B volumes at the intermediate site. You can switch operations
to your remote site (Site C), which allows the processing of data
to resume at Site C. This process is known as a failover recovery.
The Global Copy relationship between volumes at the intermediate and
the remote sites are still operational. Global Mirror continues to
operate between these two sites.
Perform the following steps after a failure has been detected at
the local site:
- Verify that the last data from the local site has been included
in a Global Mirror consistency group. Monitor this activity by querying
the B and C volumes to determine when at least two successful consistency
groups have formed. The Total Successful CG Count field
from the query output displays this information.
- Stop the Global Mirror session from which the B and C volume pairs
are included.
- Verify that the Global Mirror session has ended. Consistency groups
will not be forming when Global Mirror processing is stopped.
- Delete the Global Copy relationships between the B and C volume
pairs at the intermediate and remote sites. This prepares for reversing
the direction of the volume pair from the remote site to the intermediate
site. The cascaded relationship ends as well.
Note: When
the relationships between the B and C volumes are deleted, the cascade
parameter is disabled for the B volumes and the B volumes are no longer
detected as being in cascaded relationships.
- Issue a failover command to the B volumes with the Cascade option.
With this process, updates are collected using the change recording
feature, which allows the resynchronization of the B to A volumes.
- Create Global Copy relationships using the C and B volume pairs.
Specify the NOCOPY option.
Note: You can specify the NOCOPY
option because the B and C volume pairs contain exact copies of data.
- Use FlashCopy® to create
a copy of B source volumes to E target volumes. Specify the MODE(ASYNC)
options. This creates a backup copy of the consistency group.
- Create a Global Mirror session using the C volumes:
- Establish paths between the intended master and the intended subordinates
at the remote site.
- Define the Global Mirror session to all of the LSSs that are going
to participate in the session at the remote site.
- Join the C volumes to the Global Mirror session.
- Start the Global Mirror session from which the C, B and E volumes
are included.
- Verify that the Global Mirror session has started.
- Allow the I/O to run and monitor the formation of the consistency
groups.
- When the local site is ready to return, issue a failback command
to the B and A volumes. This command copies the changes back to the
A volumes that were made to the B volumes while hosts were running
on the B volumes. The A volumes are now synchronized with the B volumes.
- Wait for the copy operation of the B and A volumes to reach full
duplex status (all out-of-sync tracks have completed copying). You
can monitor this activity by querying the status of the B and A volume
pairs.
- End I/O processing to the C volumes.
- Verify that at least two consistency groups have formed. Assume
that consistency groups formed successfully, data in the A, B, C,
and E volumes is consistent.
- Stop the Global Mirror session between the C, B, and E volumes.
- Verify that the Global Mirror session for which the C, B, and
E volumes are included, has stopped.
- At the remote site, remove the C volumes (or Global Copy secondary
volumes) from the Global Mirror session that includes the C, B, and
E volumes.
- Delete the Global Copy relationships between the C to B volumes
between the intermediate and remote sites. Delete the Global Copy
relationships between the C to B volume pairs prepares for restoring
to the original Global Copy relationships between the B to C volume
pairs, which is described in step 23. The cascaded
relationship ends, as well.
- Issue a failover command to the A volumes. This process ends the
Metro Mirror relationships between the B and A volumes and establishes
the Metro Mirror relationships between the A and B volume pairs.
- Reestablish paths (that were disabled by the freeze operation)
between the local site LSS and intermediate site LSS that contain
the B to A Metro Mirror volume pairs.
- Issue a failback command to the A and B volumes. This command
copies the changes back to the A volumes that were made to the B volumes
in Metro Mirror relationships while hosts were running on the B volumes.
The A volumes are now synchronized with the B volumes.
- Establish the B and C volume pairs in Global Copy
relationships. Specify the NOCOPY and Cascade options.
- Optionally, you can issue a FlashCopy operation
to create a backup copy of all the C, B, and E volumes from which
the last consistency group was created. If you need to preserve data
from the set of volumes (or consistency group) at was created using
the E volumes, allow the background copy from the FlashCopy process to complete
before you continue to the next step, which describes removing the FlashCopy relationship between
the B to E volume pairs.
- Delete the FlashCopy relationship
between the B and E volume pairs to end the relationship at the intermediate
site.
- Resume Global Mirror at the intermediate site. This starts Global
Mirror processing for the B, C , and D volumes.
- Resume I/O on A volumes.
- Verify that consistency groups are forming successfully.