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In a three-site Metro/Global Mirror, if an outage occurs, a backup site is maintained regardless of

which one of the sites is lost. Suppose that an outage occurs at the local site, Global Mirror continues

to mirror updates between the intermediate and remote sites, maintaining the recovery capability at

the remote site. If an outage occurs at the intermediate site, data at the local storage system is not

affected. If an outage occurs at the remote site, data at the local and intermediate sites is not

affected. Applications continue to run normally in either case.
With the incremental resynchronization function enabled on a Metro/Global Mirror configuration, if the

intermediate site is lost, the local and remote sites can be connected, and only a subset of changed

data is copied between the volumes at the two sites. This process reduces the amount of data

needing to be copied from the local site to the remote site and the time it takes to do the copy.

Multiple Target PPRC

Provides an enhancement to disaster recovery solutions by allowing data to be mirrored from a single

primary site to two secondary sites simultaneously. The function builds on and extends Metro Mirror

and Global Mirror capabilities. Various interfaces and operating systems support the function.

Disaster recovery scenarios depend on support from controlling software such as Geographically

Dispersed Parallel Sysplex (GDPS) and IBM Copy Services Manager.

z/OS Global Mirror

If workload peaks, which might temporarily overload the bandwidth of the Global Mirror configuration,

the enhanced z/OS Global Mirror function initiates a Global Mirror suspension that preserves primary

site application performance. If you are installing new high-performance z/OS Global Mirror primary

storage subsystems, this function provides improved capacity and application performance during

heavy write activity. This enhancement can also allow Global Mirror to be configured to tolerate longer

periods of communication loss with the primary storage subsystems. This enables the Global Mirror to

stay active despite transient channel path recovery events. In addition, this enhancement can provide

fail-safe protection against application system impact that is related to unexpected data mover

system events.
The z/OS Global Mirror function is an optional function.

z/OS Metro/Global Mirror Incremental Resync

z/OS Metro/Global Mirror Incremental Resync is an enhancement for z/OS Metro/Global Mirror. z/OS

Metro/Global Mirror Incremental Resync can eliminate the need for a full copy after a HyperSwap

situation in 3-site z/OS Metro/Global Mirror configurations. The storage system supports z/OS Metro/

Global Mirror that is a 3-site mirroring solution that uses IBM System Storage Metro Mirror and z/OS

Global Mirror (XRC). The z/OS Metro/Global Mirror Incremental Resync capability is intended to

enhance this solution by enabling resynchronization of data between sites by using only the changed

data from the Metro Mirror target to the z/OS Global Mirror target after a HyperSwap operation.
If an unplanned failover occurs, you can use the z/OS Soft Fence function to prevent any system from

accessing data from an old primary PPRC site. For more information, see the GDPS/PPRC Installation

and Customization Guide, or the GDPS/PPRC HyperSwap Manager Installation and Customization

Guide.

z/OS Global Mirror Multiple Reader (enhanced readers)

z/OS Global Mirror Multiple Reader provides multiple Storage Device Manager readers that allow

improved throughput for remote mirroring configurations in IBM Z environments. z/OS Global Mirror

Multiple Reader helps maintain constant data consistency between mirrored sites and promotes

efficient recovery. This function is supported on the storage system running in a IBM Z environment

with version 1.7 or later at no additional charge.

Interoperability with existing and previous generations of the DS8000 series
All of the remote mirroring solutions that are documented in the sections above use Fibre Channel as the

communications link between the primary and secondary storage systems. The Fibre Channel ports that

are used for remote mirror and copy can be configured as either a dedicated remote mirror link or as a

shared port between remote mirroring and Fibre Channel Protocol (FCP) data traffic.
The remote mirror and copy solutions are optional capabilities and are compatible with previous

generations of DS8000 series. They are available as follows:

Chapter 3. Data management features 49