128 DS8000 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)
DS8000 storage complexes support z/OS Global Mirror only on zSeries hosts. The z/OS
Global Mirror function mirrors data on the storage unit to a remote location for disaster
recovery. It protects data consistency across all volumes that you have defined for mirroring.
The volumes can reside on several different storage units. The z/OS Global Mirror function
can mirror the volumes over several thousand kilometers from the source site to the target
recovery site. With z/OS Global Mirror, you can suspend or resume service during an outage.
You do not have to terminate your current data-copy session. You can suspend the session,
then restart it. Only data that changed during the outage needs to be re-synchronized
between the copies. The z/OS Global Mirror function is an optional function. To use it, you
must purchase the remote mirror for z/OS 2244 function authorization model, which is 2244
Model RMZ.
Note: When you implement Global Mirror, you set up 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 Utilities), 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.
