DS8000 Four site replication with Copy Services Manager

The IBM DS8000 storage products support various types of copy services which can be easily used to design two, three and four site replication solutions. In addition to the former Metro Global Mirror three site cascaded topology, the DS8870 and later models also support three site Multi Target PPRC topologies, which provide much more flexibility and can be combined with cascaded Global Copy or Global Mirror to compose a four site replication topology.

IBM Copy Services Manager (CSM), or former TPC-R for Replication (TPC-R) is the central IBM software product to manage all the various types of copy services, not only for the DS8000, but also for the majority of other IBM storage products like the Storwize Family, XIV and Flash Systems.

While CSM supports three site replication topologies for DS8000, it does not have a built in Session topology for a cascaded four site topology yet. There are various concepts for a four site replication solution, mainly depending on the customer requirements. Nevertheless, CSM manages copy services in a way that allows to combine (cascade) multiple sessions which manage the same set of volumes in a specific role of those sessions. However, this introduces implications and limitations for CSM Session management and various Failover Failback scenarios that might be required.

This Whitepaper describes a specific four site replication solution and shows how this can be managed with a set of CSM Sessions, while preventing full copies when active CSM Sessions needs to be toggled with inactive sessions to manage specific scenarios in the reversed direction.

It also provides best practices how configuration changes can be managed in such an environment to avoid configuration mistakes in CSM, by leveraging CSM features such as volume protection, site awareness and session configuration export/import capabilities.

DS8000 Four site Replication management with CSM v1.0.pdf

As an addendum, further scenarios have been developed and verified to maintain and optionally restore golden copies when performing planned or unplanned side switches. When a site planned switch is performed, there might be the requirement for a staged production start. For instance, upon a planned site switch, Global Mirror should be restarted into opposite direction to re-establish remote data center protection before starting production in the recovery data center. At the same time, golden copies should be maintained at either data center which can be used to restore the last consistent data prior the switch was performed. These are safety copies which are only held until production switch has been confirmed successfully. In case something goes wrong during the production start in the new data center, the golden copies can be restored for another start attempt. In worst case, production can be switched back to original data center and the golden copy there can be used for another start attempt.

These additional procedures can be found in the document 'CSM 4 site replication Golden Copy scenarios.pdf'

CSM 4 site replication Golden Copy scenarios.pdf