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# Understanding SRDF/Metro Smart DR

SRDF/Metro Smart DR is a two-region high available (HA) disaster recovery (DR) solution. It integrates SRDF/Metro and SRDF/A enabling HA DR for a Metro session.

A session or environment name uniquely identifies each smart DR environment . It is composed of three arrays (MetroR1 array, MetroR2 array, DR array). All arrays contain the same number of devices and all device pairings form a triangle.

The MetroR1 array contains:

- One Metro SRDF Group that is configured to the MetroR2 array (MetroR1_Metro_RDFG)
- One DR SRDF Group that is configured to the DR array (MetroR1_DR_RDFG)
- Devices that are concurrent SRDF and are paired using MetroR1_Metro_RDFG and MetroR1_DR_RDFG.

The MetroR2 array contains:

- One Metro SRDF Group that is configured to the MetroR1 array (MetroR2_Metro_RDFG)
- One DR SRDF Group that is configured to the DR array (MetroR2_DR_RDFG).
- Devices that are concurrent SRDF and are paired using MetroR2_Metro_RDFG and MetroR2_DR_RDFG.

The DR array contains one DR SRDF Group that is configured to the MetroR1 array (DR_MetroR1_RDFG).

Unisphere supports the setup, monitoring, and management of a smart DR configuration using both UI and REST API.

Unisphere blocks attempts at using smart DR SRDF groups for other replication sessions, and also blocks certain active management on smart DR SRDF groups, including device expansion and adding new devices. This limitation can be overcome by temporarily deleting the Smart DR environment to perform these operations. Replication is never suspended so Recovery Point Objective (RPO) is not affected.

Unisphere blocks attempts at SRDF active management of storage groups that are part of a smart DR environment.