Recovering from a disaster using Global Mirror

This task lists the high-level steps that you must complete in order to recover from a disaster using Global Mirror processing.

A failure at the local or primary site stops all I/O to and from the local storage server. The local server cannot communicate with the remote sites. This might impact the formation of consistency groups, because the entire process is managed and controlled by the master storage server, which is the primary storage server.

Your initial goal is to swap operations between the local and remote sites and then restart the applications. This requires that you make available a set of consistent volumes at the remote site, before the application can restart at the remote site.

When the local site is operational again, you want to return processing to the local site. Before you can return processing to the local site, you must apply changes from the remote site to the local site. These changes are the transactions that occurred after you started failover processing to the remote site.

The following considerations can help you determine where transactions are being processed:

The local site contains A volumes (the source volume), which are copied to the recovery site using Global Copy
The recovery (or remote) site contains B volumes (the target volume and FlashCopy source volume) and C volumes (the FlashCopy target volume)
A storage unit at the local site is designated as the Global Mirror master and all other local (or production) storage units are designated as subordinate storage units. The master storage unit sends commands to its subordinate storage units. These subordinates work together to create a consistency group and to communicate the FlashCopy commands to the recovery (or remote) site. All status is relayed back to the Global Mirror master.

To recover from a disaster, you must perform the following high-level tasks using the Global Mirror function and the DS CLI commands:

Note: You can also refer to a scenario that the steps have referenced in this task by referring to Using Global Mirror for an unplanned failover and failback.

End Global Mirror processing when a disaster occurs.
See Ending Global Mirror processing when a disaster occurs for additional substeps.
Check the status of the current processing for Global Mirror transactions. See Checking Global Mirror transaction status in a disaster situation for additional substeps.
Initiate the failover process of A volumes to B volumes. See Initiating failover processing for B volumes to A volumes for additional substeps.
Analyze the consistency group status. See Analyzing and validating the consistency group state for additional substeps.
Use the revertflash command to correct FlashCopy relationships. See Using the revertflash command to correct FlashCopy relationships for additional substeps.
Use the commitflash command to correct FlashCopy relationships. See Using the commitflash command to correct FlashCopy relationshipsfor additional substeps.
Initiate the fast reverse restore process. See Using fast reverse restore processing to create consistency for additional substeps.
Wait for the background copy to complete. See Waiting for the background copy to complete for additional substeps.
Reestablish the FlashCopy relationships, B volumes to C volumes. See Reestablishing the FlashCopy relationships between B volumes and C volumes for additional substeps.
Prepare to reinstate production at the local site. See Preparing to reinstate production at the local site for additional substeps.
Resynchronize the volumes. See Resynchronizing the volumes for additional substeps.
Query for first pass and drain time out-of-synch zero value and quiesce your system. See Querying, quiescing, and querying for additional substeps.
Reestablish the remote mirror and copy paths, A site to B site. See Reestablishing remote mirror and copy paths (site A to site B) for additional substeps.
Perform Global Copy failover processing to the A volumes. See Performing Global Copy failover processing to the A volumes for additional substeps.
Perform Global Copy failback processing for the A volumes. See Performing Global Copy failback processing for the A volumes for additional substeps.
Resume Global Mirror processing at site A. See Resuming Global Mirror processing at site A for additional substeps.

Ending Global Mirror processing when a disaster occurs
Complete this task to end Global Mirror processing when a disaster occurs. This is the first step in the Global Mirror disaster recovery process.
Checking Global Mirror transaction status in a disaster situation
Complete this task to check the status of your Global Mirror transactions before processing ends as a result of a disaster. Normally, this is the second step in the Global Mirror failover recovery process because in a rolling disaster, your primary server is still operational. This might be the first step if your primary server is not operational.
Initiating failover processing for B volumes to A volumes
Complete this task to perform failover processing for B volumes to A volumes so that the B volumes become the primary volumes and A volumes become the secondary volumes. The Global Copy state of the B volumes changes from secondary to primary and suspended. This is the next step after you obtain a status of your Global Mirror transactions in the Global Mirror failover recovery process.
Analyzing and validating the consistency group state
Complete this task to analyze and validate the consistency group state. This is the fourth step in the Global Mirror failover recovery process.
Using the revertflash command to correct FlashCopy relationships
Complete this task to correct the revertible states and FlashCopy sequence numbers that require the use of the DS CLI revertflash command. This is the fifth step in the Global Mirror failover recovery process unless your corrections require the use of the commitflash DS CLI command. In this case, the use of the commitflash command becomes your fifth step.
Using the commitflash command to correct FlashCopy relationships
Complete this task to correct the revertible states and FlashCopy sequence numbers that require the use of the DS CLI commitflash command. This is the fifth step in the Global Mirror failover recovery process unless your corrections require the use of the revertflash DS CLI command. In this case, the use of the revertflash command becomes your fifth step.
Using fast reverse restore processing to create consistency
Complete this task to create the same consistent data on the B volumes that you have on the C volumes. The fast reverse restore option allows you to reverse a FlashCopy relationship without waiting for the background copy of a previous FlashCopy operation to finish. This is the sixth step in the Global Mirror disaster recovery process.
Waiting for the background copy to complete
Complete this task to determine when all fast reverse restore operations are complete and when no more FlashCopy relationships exist between the B volumes and the C volumes. This is the seventh step in the Global Mirror disaster recovery process.
Reestablishing the FlashCopy relationships between B volumes and C volumes
Complete this task to reestablish the FlashCopy relationships between your B volumes and C volumes. This is the eighth step in using the Global Mirror disaster recovery process.
Preparing to reinstate production at the local site
Complete this task to begin the process of returning production to your local site. Just as there was a series of steps in the failover recovery process to your remote site, there are a series of steps that you must take to return production to your local site.
Resynchronizing the volumes
Complete this task to resynchronize the volumes, B volumes to A volumes. This is the second step in the failback recovery process that allows production to be returned to your A site.
Querying, quiescing, and querying
Complete this task series to query for the first pass of the out-of-sync bitmap completion, to quiesce your system, and to complete the query process to ensure that the out-of-sync tracks equal 0. This series of tasks is the third step in the failback recovery process that allows production to be returned to your A site.
Reestablishing remote mirror and copy paths (site A to site B)
Complete this task to reestablish the remote mirror and copy paths between site A and site B in preparation for the transfer of operations from the B site to the A site. This is the fourth step in the failback disaster recovery process.
Performing Global Copy failover processing to the A volumes
Complete this task to perform failover processing from A volumes to B volumes so that the A volumes become the primary volumes and B volumes become the secondary volumes. This is the fifth step in the failback recovery process.
Performing Global Copy failback processing for the A volumes
Complete this task to perform Global Copy failback processing for the A volumes. This process resynchronizes the volumes at Site A with volumes at Site B and restarts mirroring from site A (local site) to site B (remote site). This is the sixth step in the failback recovery process.
Resuming Global Mirror processing at site A
Complete this task to start or resume Global Mirror processing at the A site. This is the final step in the failback recovery process.