HP StorageWorks Continuous Access EVA Administrator Guide (T3687-96043, December 2005)

Bidirectional r
eplication
When an array co
ntains both source virtual disks and destination virtual disks, it is bidirectional. An
array can have a bidire ctional data replication relationship with up to two other arrays. Individual virtual
disks can have only unidirectional relationships with o ne other virtual disk.
DR groups
A data replication (DR) group is a named group of virtual dis ks selected from one or more disk groups
so that they remotely replicate to the same destination, fail over tog ether, share a log, and preserve
write order within the group. For example, all the virtual disks used by one application instance must
be in one DR group. The maximum number of virtual disks in a DR group and the maximum number
of DR groups per array vary with the controller software version. For current supported limits, see the
latest release notes.
DR groups occur in pairs, the source DR group containing the source virtual disks and the destination DR
group c ontaining the destination virtual disks. (Source and destination pairs are also known as copy sets.)
Hosts write data to the virtual disks in the source DR group and the array software copies the d ata to the
virtual disks in the destination DR group. When a DR group fails over, the roles reverse. The destination
DR group becom es the sourc e, and the original source DR group bec om es the n ew destination.
The D R group state indicates the role of the DR group relative to its initial role. When the source is the
same array that was the sourc e when the DR group was created, the DR groups are in an original state.
When replication oc curs from an array that was created as a destination, the DR group state is failed over.
Figure 1 depicts the replication of one DR group between local and remote sites.
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