How to resume normal operations after Disaster ?

 

Disaster strikes.  In this example, a backhoe has dug up the network cables that connect the data Center to clients.  The Data Center volume (dc_vol) is unavailable.

From the Disaster Recovery Site, break the mirror and the SnapMirror replica becomes writable.

The syntax of the snapmirror break command is:

destination>snapmirror break destination_vol.

After breaking the mirror, direct clients to the Disaster Recovery volume (dr_vol), and they continue reading and writing their data.

The Data Center volume is offline and becoming out of data.  The last shared Snapshot copy is preserved, however.  After the problem is fixed, a combination of snapmirror resync and snapmirror break commands will help you to resume normal operations.

Re-establish Normal Operations 1

With the problem fixed, you can now move the new production data to the Data Center with the snapmirror resync command executed from the Data Center storage system. 

The syntax of the snapmirror resync command is: destination>snapmirror resync destination_vol.

Executing the snapmirror resync command from the Data Center storage system has the effect of  reversing the direction of the SnapMirror relationship.  The Data Center storage system is now the destination storage system; the Data Center volume (dc_vol) is now the destination volume.  The Disaster Recovery Center volume is now the source of the new production data written while the Data Center storage system was offline.

While the Data Center source volume is receiving data from the snapmirror resync operation, clients are still accessing their data from the disaster recovery site.

Re-establish Normal Operations 2

The next step in re-establishing normal operations is to stop user access to the disaster recovery volume and complete the update of the Data Center volume with any production data written since the beginning of the snapmirror resync command.

Execute the snapmirror update command from the Data Center storage system.

The syntax of the command is:  

destination>snapmirror update –S source:source_volume destination_vol.

(In our example, the Data Center storage system became the destination when the snapmirror resync command was used to move the Disaster Recovery production data to the Data Center storage system.)

Re-establish Normal Operations 3

The Data Center volume (dc_vol) has all of the production data; however, at this point dc_vol is a read-only SnapMirror replica of dr_vol, the Disaster Recovery volume. You must now reverse the direction of the SnapMirror relationship by breaking the mirror with the SnapMirror break command executed from the Data Center storage system.

The syntax of the snapmirror break command is:

destination>snapmirror break destination_vol.

Re-establish Normal Operations 4

The final step to resuming normal operations is to execute the snapmirror resync command from the Disaster Recovery site.

The syntax of the snapmirror resync command is:

destination>snapmirror resync destination_vol.

This final SnapMirror resync command executed from the Disaster Recovery Site will return SnapMirror to the original source and destination relationship.