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Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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Failback to source

After a failover (planned or unplanned), use the failback command to resume normal SRDF operations by initiating read/write operations on the source (R1) devices, and stop read/write operations on the target (R2) devices.

Failback initiates the following activities for each specified SRDF pair in a device group:

  1. The target (R2) device is write disabled to its local hosts.
  2. Traffic is suspended on the SRDF links.
  3. If the target side is operational, and there are invalid remote (R2) tracks on the source side (and the force option is specified), the invalid R1 source tracks are marked to refresh from the target side.
  4. The invalid tracks on the source (R1) side are refreshed from the target R2 side. The track tables are merged between the R1 and R2 sides.
  5. Traffic is resumed on the SRDF links.
  6. The source (R1) device is read/write enabled to its local hosts.

    The target (R2) devices become read-only to their local hosts.

Failback includes the following general steps:

  1. Stop I/Os on the failover host at site B.
  2. Make all R2 devices in the array at site B Not Ready or Read Only (Write Disabled) to the host.
  3. If the array at site A was powered off, ensure that SRDF links between array A and array B are disabled before powering on the array at site A.
  4. Power on the array at site A and make R1 devices Read/Write enabled to the production host.
  5. Enable the SRDF links between the array at site A and the array at site B.
  6. Bring the SRDF links online and restart the local host. The R1 devices automatically receive data from the R2 devices which accumulated invalid tracks on their R2 SRDF mirrors during production processing.
  7. Once all SRDF pairs are synchronized, enable consistency groups on the SRDF links between the array at site A and the array at site B.
  8. Restart the site A host and applications.

The following image shows the failback of an SRDF pair.

Figure 1. Failback of an SRDF device
NOTE:

When you issue the symrdf command, device external locks are set on all SRDF devices you are about to establish. See Device external locks and Table 1.

Syntax

Use failback for a device group, composite group, storage group, or device file: 

symrdf -g DgName failback
symrdf -cg CgName failback
symrdf -cg SgName failback
symrdf -f[ile] FileName failback
NOTE:

The R2 may be set to read/write disabled (not ready) by setting the value of SYMAPI_RDF_RW_DISABLE_R2 to ENABLE in the options file. For more information, refer to the Dell Solutions Enabler CLI Reference Guide

Examples

To initiate a failback on all the SRDF pairs in the prod device group:

symrdf -g prod failback

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