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# Manage remote replication sessions

Unisphere supports the monitoring and management of SRDF replication on storage groups directly without having to map to a device group.

The SRDF dashboard provides a single place to monitor and manage SRDF sessions on a storage system, including device groups types R1, R2, and R21.

See the Dell SRDF Introduction Guide for an overview of SRDF.

Unisphere allows you to monitor and manage SRDF/Metro from the SRDF dashboard. SRDF/Metro delivers active/active high availability for non-stop data access and workload mobility – within a data center and across metro distance. It provides array clustering for storage systems enabling even more resiliency, agility, and data mobility. SRDF/Metro enables hosts and host clusters to directly access a LUN or storage group on the primary SRDF array and secondary SRDF array (sites A and B). This level of flexibility delivers the highest availability and best agility for rapidly changing business environments.

In a SRDF/Metro configuration, SRDF/Metro uses the SRDF link between the two sides of the SRDF device pair to ensure consistency of the data on the two sides. If the SRDF device pair becomes Not Ready (NR) on the SRDF link, SRDF/Metro must respond by choosing one side of the SRDF device pair to remain accessible to the hosts, while making the other side of the SRDF device pair inaccessible. There are two options which enable this choice: Bias and Witness.

The first option, Bias, is a function of the two storage systems taking part in the SRDF/Metro and is a required and integral component of the configuration. The second option, Witness, is an optional component of SRDF/Metro which allows a third storage system to act as an external arbitrator to avoid an inconsistent result in cases where the bias functionality alone may not result in continued host availability of a surviving nonbiased array.