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Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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Establish an SRDF pair (incremental)

An incremental establish re-synchronizes data on the source (R1) and target (R2) device when:
  • a split RDF pair is rejoined.
  • device pairs are made Read-Write (RW) on the SRDF link after having been Not Ready (NR) on the link.
Only the data that was updated on the source (R1) device while the SRDF pair was split or suspended is copied, greatly reducing the amount of data that is to be transferred.

An incremental establish initiates the following activities for each specified SRDF pair in a device group:

  • The target (R2) device is write disabled to its local host I/O.
  • Traffic is suspended on the SRDF links.
  • The invalid tracks on the target (R2) device are refreshed from the changed tracks of the source (R1) device.
  • The track tables are merged between the source (R1) device and the target (R2) device.
  • Traffic is resumed on the SRDF links.

In SRDF/S configurations, when the establish operation completes and the device pair is in the Synchronized state, the source (R1) device and the target (R2) device contain identical data.

In SRDF/A configurations, when the establish operation completes and the device pair is in the Consistent state, the target (R2) device contains dependent write consistent data.

In SRDF/Metro configurations, once the source (R1) device and the target(R2) device contain identical data, the pair state is changed to either ActiveActive or ActiveBias and the R2 side is made RW-accessible to the host(s).

The following image shows an incremental establish of an SRDF pair.

Figure 1. SRDF establish (incremental)
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 incremental establish for a device group, composite group, storage group, or device file: 

symrdf -g DgName establish
symrdf -cg CgName establish
symrdf -sg SgName establish
symrdf -f[ile] FileName establish

These commands do not include an option to definition the type of establish operation, because incremental is the default for this operation.

Include the -use_bias option in SRDF/Metro configurations to indicate that neither the Witness method nor vWitness methods of determining bias is used: 

symrdf -g DgName establish -use_bias
symrdf -cg CgName establish -use_bias
symrdf -sg SgName establish -use_bias
symrdf -f[ile] FileName establish -use_bias
NOTE:For SRDF/Metro configurations:
  • The establish operation must include all devices in the SRDF/Metro group.
  • If the Witness method is used to determine which side of the device pair remains accessible to the host, the Witness groups must be online or the vWitness must be accessible to both sides.
NOTE:

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 an incremental establish on all SRDF pairs in the prod device group:

symrdf -g prod establish

To initiate an incremental establish for a list of SRDF pairs in SRDF/Metro group 86 where bias determines which side of the device pair remains accessible to the host:

symrdf -f /tmp/device_file -sid 085 -rdfg 86 establish -use_bias

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