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102 DS6000 Series: Concepts and Architecture
The data at the remote site is current within 3 to 5 seconds, but this recovery point (RPO)
depends on the workload and bandwidth available to the remote site.
In contrast to the previously mentioned Global Copy solution, Global Mirror overcomes its
disadvantages and automates all of the steps that have to be done manually when using
Global Copy.
If you use Global Mirror, you must adhere to the following additional rules:
You must purchase a Point-in-Time Copy function authorization (2244 Model PTC) for the
secondary storage unit.
If Global Mirror will be used during failback on the secondary storage unit, you must also
purchase a Point-in-Time Copy function authorization for the primary system.
z/OS Global Mirror (XRC)
z/OS Global Mirror is an asynchronous copy function for the z/Series environment. This
function has a different architecture than Global Mirror. The DS6000 can only be used as a
secondary system for z/OS Global Mirror (it cannot be used as primary system).
Note: When you implement Global Mirror, you setup the FlashCopy between the B and C
volumes with
No Background copy and Start Change Recording options. It means that
before the latest data is updated to the B volumes, the last consistent data in the B volume
is moved to the C volumes. Therefore, at some time, a part of consistent data is in the B
volume, and the other part of consistent data is in the C volume.
If a disaster occurs during the FlashCopy of the data, special procedures are needed to
finalize the FlashCopy.
In the recovery phase, the consistent copy is created in the B volumes. You need some
operations to check and create the consistent copy.
You need to check the status of the B volumes for the recovery operations. Generally, these
check and recovery operations are complicated and difficult with the GUI or CLI in a
disaster situation. Therefore, you may want to use some management tools (for example,
Global Mirror Utility), or management software (for example, Multiple Device Manager
Replication Manager), for Global Mirror to automate this recovery procedure.
Note: PPRC can do failover and failback operations. A failover operation is the process of
temporarily switching production to a backup facility (normally your recovery site) following
a planned outage, such as a scheduled maintenance period, or an unplanned outage,
such as a disaster. A failback operation is the process of returning production to its original
location. These operations use Remote Mirror and Copy functions to help reduce the time
that is required to synchronize volumes after the sites are switched during a planned or
unplanned outage.