IBM DS8000 User Manual page 54

Persistent FlashCopy
Refresh target volume
Resynchronizing FlashCopy volume pairs
Reverse restore
Remote mirror and copy
The remote mirror and copy feature is a flexible data mirroring technology that
allows replication between a source volume and a target volume on one or two
disk storage units. You can also issue remote mirror and copy operations to a
group of source volumes on one logical subsystem (LSS) and a group of target
volumes on another LSS. (An LSS is a logical grouping of up to 256 logical
volumes for which the volumes must have the same disk format, either count key
data or fixed block.)
Remote mirror and copy is an optional feature that provides data backup and
disaster recovery. To use it, you must purchase at least one of the remote mirror
and copy 2244/239x function authorization features. DS8000 storage units can
participate in remote mirror and copy solutions with the DS6000 series, ESS Model
750, and ESS Model 800.
The remote mirror and copy feature provides synchronous (Metro Mirror) and
asynchronous (Global Copy) data mirroring. The main difference is that the Global
Copy feature can operate at very long distances, even continental distances, with
minimal impact on applications. Distance is limited only by the network and
channel extenders technology capabilities. The maximum supported distance for
Metro Mirror is 300 km.
With Metro Mirror, application write performance is dependent on the available
bandwidth. Global Copy allows you to better use your available bandwidth
capacity, therefore allowing you to include more of your data to be protected.
The enhancement to Global Copy is Global Mirror, which uses Global Copy and
the benefits of FlashCopy to form consistency groups. (A consistency group is a set
of volumes that contain consistent and current data to provide a true data backup
at a remote site.) Global Mirror uses a master storage unit (along with optional
subordinate storage units) to internally, without external automation software,
manage data consistency across volumes using consistency groups.
Consistency groups can also be created using the freeze and run functions of Metro
Mirror. The freeze and run functions, when used with external automation
software, provide data consistency for multiple Metro Mirror volume pairs.
The following sections describe the remote mirror and copy functions.
Synchronous mirroring (Metro Mirror)
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DS8000 User's Guide
Allows the FlashCopy relationship to remain even after the FlashCopy
operation completes. You must explicitly delete the relationship.
Provides the ability to refresh a FlashCopy relationship, without recopying
all tracks from the source volume to the target volume.
Provides the ability to update an initial point-in-time copy of a source
volume without having to recopy your entire volume.
Reverses the FlashCopy relationship and copies data from the target
volume to the source volume.
Provides real-time mirroring of logical volumes (a source and a target)