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Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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Planned workload switching: Cascaded SRDF/Star

About this task

Maintenance, testing and other activities may require switching the production workload site to another site.

This section describes the steps to switch workload sites when the operation can be scheduled in advance.

This operation requires you to:

  • Stop the workload at the current production site,
  • Halt the SRDF/Star environment (draining and synchronizing both remote sites in order for all three sites to have the same data), and
  • Switching the production workload site to one of the remote sites.

When switching the workload to the synchronous target site, you can transition to the STAR Protected state.

There is limited support for this configuration.

When configured as Cascaded SRDF with the workload at London:

  • Only the asynchronous link can be protected.
  • The synchronous link (NewJersey -> NewYork) can only be connected.
  • SRDF/Star cannot be enabled at London.

At the end of the switch operation the system comes up in the same STAR mode of operation that was configured before the switch operation was initiated.

Steps

  1. At the current workload site (NewYork), perform the SRDF/Star halt action.

    To halt CG StarGrp: 

    symstar -cg StarGrp halt

    The halt action:

    • Disables the R1 devices,
    • Waits for all invalid tracks and cycles to drain,
    • Suspends the SRDF links,
    • Disables SRDF consistency protection, and
    • Sets the STAR mode indicators.

    The target sites transition to the Halted state, with all three sites having the data.

    Figure 1. Cascaded SRDF/Star: halted
  2. From a Star control host at the synchronous target site (NewJersey), issue the switch command to switch the workload to the synchronous target site (NewJersey). 
    symstar -cg StarGrp switch -site NewJersey

    The following image shows the resulting SRDF/Star state:

    Figure 2. Cascaded SRDF/Star: switched workload site
    NOTE:

    The entire SRDF/Star environment can also be halted from a non-workload site.

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