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SRDF device used for Concurrent SRDF environments =R21

SRDF device used for SRDF/Star environments =R11

SRDF device used for Cascaded SRDF environments =R22

A dual personality SRDF device is a device that can act as both an R1 and an R2 device in different SRDF configurations. There are three types of dual personality SRDF devices: R21, R11, and R22.

• An R21 device is an R2 device that is paired with another R1 device in a different SRDF group. This allows the R21 device to receive updates from the primary site and send updates to the secondary site. An R21 device is used for Concurrent SRDF environments, which provide simultaneous disaster recovery and data migration capabilities.For example, an R21 device can be used to migrate data from one array to another while maintaining a synchronous copy of the data on a third array.1
• An R11 device is an R1 device that is paired with another R1 device in a different SRDF group. This allows the R11 device to receive updates from the primary site and send updates to the tertiary site. An R11 device is used for SRDF/Star environments, which provide three-site disaster recovery capabilities with a single hop between any two sites.For example, an R11 device can be used to create a synchronous copy of the data on a secondary site and an asynchronous copy of the data on a tertiary site.2
• An R22 device is an R2 device that is paired with another R2 device in a different SRDF group. This allows the R22 device to receive updates from the secondary site and send updates to the tertiary site. An R22 device is used for Cascaded SRDF environments, which provide three-site disaster recovery capabilities with two hops between the primary and tertiary sites.For example, an R22 device can be used to create an asynchronous copy of the data on a secondary site and another asynchronous copy of the data on a tertiary site.3

References:

• Dell EMC SRDF Introduction - Dell Technologies Partner Portal
• Dell EMC PowerMax and VMAX All Flash: SRDF Product Guide
• Dell EMC PowerMaxOS Performance Guide

An SRDF/Metro device pair was in an ActiveActive state, meaning that both the R1 and R2 devices were read/write accessible to the host or hosts. A link failure between arrays occurs, causing the device pair to become Not Ready (NR) on the SRDF link. SRDF/Metro responds by making the non-biased or R2 paired device inaccessible (not ready) to the host or host cluster, while keeping the biased or R1 paired device accessible (ready). This ensures that there is no data inconsistency or split-brain scenario between the two sites. The device pair enters an Active Bias state, which indicates that only one side of the pair is active and has a bias attribute set. The bias attribute determines which side of the pair remains accessible in case of a link failure. By default, the bias is set to the R1 side of the pair, but it can be changed using the symrdf set bias command. The application continues running on the R1 side, and the link failure is addressed. Once the link is restored, the device pair resumes the ActiveActive state and both devices become accessible again.

References:

• SRDF/Metro overview
• VMware vSphere Metro Storage Cluster (vMSC) with Dell PowerMax and Dell EMC VMAX SRDF/Metro
• Understanding bias

If an administrator implemented SYMACLs on a PowerMax using host-based Access IDs and is no longer able to run SYMCLI commands against the volumes belonging to a host, one possible reason could be that the SYMAPI options file was manually modified with the wrong host ID. The SYMAPI options file contains configuration settings for Solutions Enabler, including host IDs for access control. If this file is incorrectly modified, it could prevent the administrator from running SYMCLI commands against certain volumes34. References: Dell EMC PowerMax and VMAX All Flash: Embedded Management, Role Based Access Control on PowerMax – Storage Intelligence