Metro/Global Mirror primary site unplanned outage – site swap to intermediate site

This scenario provides a disaster recovery solution if a failure occurs at your local site. You can run your operations from your intermediate site, which is protected by a two-site Global Mirror configuration, until your local site has recovered. Global Mirror continues sending updates to the storage unit at the remote site and continues to form consistency groups.

If an unplanned outage occurs, use the following process to perform failover and restore operations to the intermediate site.

1. At the local site, ensure that data consistency is achieved between the A and B volume pairs. Assume that the local site was not completely destroyed, it is essential that data from any surviving A and B volume pairs be copied and a consistent copy be achieved at the remote site. To create data consistency, freeze all write activity to the Metro Mirror primary volumes. If you quiesce host I/O to the A volumes at the local site, continue to step 2. If you freeze write activity to the Metro/Mirror source volumes, perform the following steps:
   1. Freeze updates to the A volumes in the Metro Mirror relationships across the affected LSSs. This ensures that the B volumes will be consistent at the time of the freeze process.
   2. Resume operations following a freeze. This operation is also called a thaw operation and it allows I/O processing to resume for the specified volume pairs.
2. Issue a PPRC establish pair command with the failover, force, and cascade options. Specify the Remote site secondary devices (C volumes) as the primaries and the local site Metro Mirror primary devices (A volumes) as the secondaries.
3. Issue CRECOVER or PRECOVER commands to the intermediate devices (B volumes), for the Metro Mirror relationships (A-B).
4. Resume host I/O at the intermediate site.

When the A volumes are ready to return to production, complete the following steps:

1. Issue PPRC establish pair commands with the failback and force options from the remote site to the local site (site C to site A).
2. Wait for the first pass copy to complete from the remote to the local site (site C to site A), and then start the incremental resync change recording mechanism on the site B to site C pairs, with NOCOPY specified in the INCRESYNC parameter.
3. Use the RSESSION command to stop Global Mirror at the intermediate site.
4. Suspend the Global Copy pairs between the intermediate and remote sites (site B to site C pairs).
5. Wait for all data to drain from the remote site back to the local site (site C to site A). An alternate from doing queries to wait for all out of sync data to drain is to convert the site C to site A pairs to synchronous. When they become full duplex, all data has been copied.
6. Suspend the site C to site A PPRC pairs.
7. Issue CRECOVER or PRECOVER commands to the remote devices (C volumes), for the suspended site C to site B relationships.
8. Issue PPRC establish pair commands with failover and cascading to reverse the direction of the site C to site A relationships. The command is issued to the A devices.
9. Issue PPRC establish pair commands with failback to the site A to site C relationships.
10. Establish Metro Mirror using the incremental resync change recording that has been in process since the site swap to the intermediate site, with the force option, from the intermediate to the local site (issue PPRC establish pair commands with option SYNC, mode INCRES, and force from B to A).
11. Issue PPRC establish pair commands to the site B to site A relationships to start the incremental resync change recording (issue PPRC establish pair commands with mode NOCOPY and INCRESYNC(START)).
12. Wait for the site B to site A relationships to become full duplex and the site A to site C relationships to complete their first pass copy.
13. Start the Global Mirror, running from the local to the remote site in order to update the aged consistency group at the remote site.

To transition back to the original configuration (from site A to B to C), use the following process:

1. Quiesce all host I/O activity and suspend the site B to site A relationships.
2. Issue a PPRC establish pair command with the failover, force, and cascade options. Specify the remote site devices (C volumes) as the primaries and the intermediate site devices (B volumes) as the secondaries.
3. Issue CRECOVER or PRECOVER commands to the local devices (A volumes), for the site B to site A relationships
4. Resume host I/O at the local site.
5. Issue PPRC establish pair commands with the failback and force options from the remote site to the intermediate site (site C to site B).
6. Wait for the first pass copy to complete from the remote to the intermediate site (site C to site B), then start the incremental resync change recording mechanism on the site A to site C pairs, with NOCOPY specified in the INCRESYNC parameter.
7. Use the RSESSION command to stop Global Mirror at the local site.
8. Suspend the Global Copy pairs between the local and remote sites (site A to site C pairs).
9. Wait for all data to drain from the remote site back to the local site (site C to site B). An alternate from doing queries to wait for all out of sync data to drain is to convert the site C to site B pairs to synchronous. When they become full duplex, all data has been copied.
10. Issue CRECOVER or PRECOVER commands to the remote devices (C volumes) to the A to C volumes, for the suspended site C to site A relationships.
11. Suspend the site C to site B PPRC pairs.
12. Issue PPRC establish pair commands with failover and cascading to reverse the direction of the site C to site B relationships. The command is issued to the B devices.
13. Issue PPRC establish pair commands with failback to the site B to site C relationships.
14. Establish Metro Mirror by using the incremental resync change recording that has been in process since the site swap to the local site, with the force option, from the local site to the intermediate site (issue PPRC establish pair commands with option SYNC, mode INCRES, and force from site A to site B).
15. Issue PPRC establish pair commands to the site A to site B relationships to start the incremental resync change recording (issue PPRC establish pair commands with mode NOCOPY and INCRESYNC(START)).
16. Wait for the site A to site B relationships to become full duplex and the site B to site C relationships to complete their first pass copy.
17. Start the Global Mirror. Run from the intermediate to the remote site to update the aged consistency group at the remote site.

You have change the Metro/Global Mirror operations running from site A to B to C.