Extended Distance Protection

NOTE: Difference between R21 and DL R21 - The R1 SRDF mirror of the R21 device operates in adaptive copy disk mode while the R1 SRDF mirror of the DL R21 device operates in adaptive copy write pending mode between Symmetrix B and Symmetrix

Extended Distance Protection

The SRDF/Extended Distance Protection (EDP) functionality is a licensed SRDF feature that offers a long distance disaster recovery (DR) solution.

 

The SRDF/EDP is a three-site topology that requires Enginuity version 5874 or higher running on Symmetrix B and Enginuity version 5773 or higher running on Symmetrix A and Symmetrix C. CKD devices
are not supported in SRDF/EDP.

This is achieved through a cascaded SRDF setup, where a VMAX 40K or VMAX 20K/VMAX array at a secondary site uses DL R21 devices to capture only the differential data that would be owed to the tertiary site in the event of a primary site failure. It is the data on the diskless R21 devices that helps these topologies achieve a zero Recovery Point Objective (RPO).

Note: The R1 and R2 devices at each end must both be thick devices or both be thin devices. The connectivity between DL R21 devices and thin devices is supported with Enginuity version 5875.135.91 or higher. With Enginuity version 5874, only thick R1 and R2 devices can be connected to DL R21 devices.

Setting up an SRDF/EDP relationship
Setting up a SRDF/EDP relationship is a two-step process:
1. Create the DLR1 --> R2 pair between Symmetrix B and Symmetrix C.
2. Create the R1 --> DLR2 pair between Symmetrix A and Symmetrix B. Now, the configuration is R1 --> DLR21 --> R2.

Note: The first hop R1 -> R21 cannot operate in asynchronous mode.

Benefits
The benefits of SRDF/EDP are:
A long distance mirroring and disaster restart solution with the ability to achieve zero RPO at the tertiary site.
SRDF/EDP can also be implemented with SRDF/Star. SRDF/Star differential relationship support between Symmetrix A and Symmetrix C is intended for failover operations.



SRDF/Star with SRDF/EDP
Enginuity versions 5874 and higher support SRDF/EDP topologies in SRDF/Star environments. These topologies require DL R21 devices in Symmetrix B (synchronous site) and R2 or R22 devices in Symmetrix C (asynchronous site).