One of the DR Method : SRDF (Symmetrix Remote Data Facility)

SRDF (Symmetrix Remote Data Facility) is a family of EMC products that facilitates the data replication from one Symmetrix storage array to another through a Storage Area Network or IP network.

SRDF logically pairs a Logical Unit Number (LUN) or a group of LUNs from each array and replicates data from one to the other synchronously or asynchronously. An established pair of LUNs can be split, so that separate hosts can access the same data independently (maybe for backup), and then resynchronised.

In synchronous mode (SRDF/S), the primary array waits until the secondary array has acknowledged each write before the next write is accepted, ensuring that the replicated copy of the data is always as current as the primary. However, the latency due to propagation increases significantly with distance.

Asynchronous SRDF (SRDF/A) transfers changes to the secondary array in units called delta sets, which are transferred at defined intervals. Although the remote copy of the data will never be as current as the primary copy, this method can replicate data over considerable distances and with reduced bandwidth requirements and mimimal impact on host performance.

Other forms of SRDF exist to integrate with clustered environments and to manage multiple SRDF pairs where replication of multiple LUNs must be consistent (such as with the data files and log files of a database application).