IBM XIV Storage System Copy Services and Migration

5.3 Role reversalWith synchronous mirroring, roles can be modified by either switching or changing.Switching roles must be initiated on the master volume or consistency group when remotemirroring is operational. As the task name implies, it switches the master role to the slave roleand at the same time the slave role to the master role.Changing roles can be performed at any time (when a pair is active or inactive) for the slave,and for the master when the coupling is inactive. A change role reverts only the role of thatpeer.5.3.1 Switching rolesSwitching roles exchanges the roles of master and slave volumes or CGs. It can beperformed after the remote mirroring function is in operation and the pair is synchronized.After switching roles, the master volume or CG becomes the slave volume or CG and viceversa. There are two typical reasons for switching roles. These are:► Drills/DR testsDrills can be performed to test the functioning of the secondary site. In a drill, anadministrator simulates a disaster and tests that all procedures are operating smoothlyand that documentation is accurate.► Scheduled maintenanceTo perform maintenance at the primary site, operations can be switched to the secondarysite some time before the maintenance. This switchover cannot be performed if the masterand slave volumes or CG are not synchronized/consistent.Normally, switching the roles requires shutting down the servers at the primary site first,changing SAN zoning and XIV LUN masking to allow access to the secondary site volumes,and then restarting the servers with access to the secondary (remote) XIV. However, incertain clustered environments this takeover could be automated.5.3.2 Change roleIn a disaster at the primary site, a role change at the secondary site is the normal recoveryaction.Assuming that the primary site is down and the secondary site will become the mainproduction site, changing roles is performed at the remote (now production) site first. Later,when the primary site is up again and communication is reestablished you also change therole at the primary site to a slave to be able to establish remote mirroring from the secondarysite back to the normal production (primary) site.134 IBM XIV Storage System: Copy Services and Migration