Symmetrix Remote Data Facility
The Symmetrix Remote Data Facility ( SRDF ) is software from EMC² , which is intended to ensure the uninterrupted operation of important IT systems. Today it is considered the standard for company-wide applications and business processes for uninterrupted operation.
Possible applications include, for example, data warehousing , synchronization of databases in the groupware , data migration or disaster recovery .
SRDF automatically and in real time mirrors the data of a primary Symmetrix storage system on a second, spatially separated Symmetrix storage system.
SRDF originally describes a technique for replication of logical devices between two remote EMC² Symmetrix storage systems. A distinction is made between synchronous replication (SRDF / S) and asynchronous replication (SRDF / A). It was launched by EMC in 1993. In the meantime, the technology is also used to replicate between a Symmetrix and another SAN storage or an IP address .
Working method
SRDF defines logical pairs of a Logical Unit Number ( LUN ) or group of LUNs from each disk array and replicates data from one to another synchronously, semi-synchronously or asynchronously. An established pair of LUNs can be split up so that separate computers have the same data and can use them independently of one another (e.g. for data backup). Then the asynchronous status can be synchronized again.
In synchronous mode (SRDF / S) , the primary array waits until the secondary array has performed and confirmed every write operation before initiating the next write operation. This means that the replicated copy of the data is always as current as the primary. But the resulting latency increases significantly as the distance between the replication sites increases .
In semi-synchronous mode , the application receives the confirmation of the first write operation from the local cache . The second write is not performed until the previous write has been confirmed by the remote cache . This form of the SRDF is faster than the synchronous mode.
Asynchronous SRDF (SRDF / A) replications on the secondary array are contained in the delta sets , which are transmitted at defined intervals. Although the remote copy of the data is never as current as the primary copy, this method of replicating data can be used over long distances and with greatly reduced bandwidth requirements.
Other forms of SRDF implementation exist in order to integrate them into cluster environments and to keep multiple replication pairs from multiple LUNs in sync like the data and log files of a database application.