Home > Storage > PowerMax and VMAX > Storage Admin > Implementing Dell SRDF SRA with VMware SRM > SRDF overview
The Dell Symmetrix Remote Data Facility (SRDF) family of products offers a range of VMAX/PowerMax-based disaster recovery, parallel processing, and data migration solutions.
SRDF disaster recovery solutions are based on active remote mirroring and dependent-write consistent copies of data maintained at one or more remote locations. A dependent-write is a write operation that cannot be issued by an application until a prior, related write I/O operation completes. Dependent-write consistency is required to ensure transactional consistency when the applications are restarted at the remote location.
SRDF configurations require at least two VMAX/PowerMax systems. In 2-site, non-SRDF/Metro configurations, these systems are usually also known as the primary and the secondary systems. Both sites can be located in the same room, in different buildings within the same campus, or hundreds to thousands of kilometers apart.
The Dell SRDF SRA supports three modes of 2-site replication:
SRDF/Synchronous (SRDF/S) is a disaster-restart solution that operates in synchronous mode and maintains a real-time (synchronous) mirrored copy of production data (R1 devices) in a physically separated VMAX/PowerMax system (R2 devices) within an SRDF configuration. SRDF/S is a method of replicating production data changes from locations less than 200 km apart.
Synchronous replication takes writes that are inbound to the source VMAX/PowerMax and copies them to the target VMAX/PowerMax. The resources of the storage arrays are exclusively used for the copy. The write operation from the virtual machine is not acknowledged back to the host until both VMAX/PowerMax arrays have a copy of the data in their cache. SRDF/S is a building block of several multi-site disaster restart options such as SRDF/Star.
SRDF/Asynchronous (SRDF/A) mode provides a dependent write consistent copy on the target (R2) device, which is only slightly behind the source (R1) device. SRDF/A session data is transferred to the remote VMAX/PowerMax array in predefined timed cycles or delta sets, which minimizes the redundancy of same track changes being transferred over the link.
SRDF/A provides a long-distance replication solution with minimal impact on performance that preserves data consistency. In the event of a disaster at the R1 site or if SRDF links are lost during data transfer, a partial delta set of data can be discarded, preserving consistency on the R2 with a maximum data loss of two SRDF/A cycles or less.
SRDF/Metro makes R2 devices Read/Write accessible to a host (or multiple hosts in clusters). Hosts write to both the R1 and R2 sides of SRDF device pairs (Active-Active). SRDF/Metro ensures that each copy remains current and consistent.
For more information on SRDF technology, including setup and configuration, refer to Dell Symmetrix Remote Data Facility (SRDF) documentation available at http://support.dell.com.