There are unidirectional and bidirectional SRDF configurations.
Unidirectional means that with two storage systems all source units are located in one storage system and all target units in the other.
In bidirectional configurations, each storage system has both source and target units.
Each system that uses SRDF units in normal remote copy mode must generate the source units in the usual way. The target units must be generated for each system that is to access them. If the same system is to access source and target units, both must be generated on the system. It is then possible to access the target units if the storage system with the source units fails.
The figure below shows a unidirectional remote copy configuration for SRDF (simplified diagram). The local storage system contains all the source units. It is connected to the remote storage system over two remote links. The remote storage system contains all the target units.
This example shows only one source unit, one target unit and two remote links: RA 5B and 12B of the local storage system are linked to RA 3B and 14B of the remote storage system.
Remote copy mode is indicated by the black arrows. The local system in the local Data Center accesses the source unit. The target unit is accessed via the remote links. If the local Data Center fails in the event of a disaster, processing can be continued on the standby system (gray arrows). The standby system in the remote Data Center accesses the target unit.
Figure 22: Unidirectional remote copy configuration (SRDF)