Converting from multi-target to Cascaded replication in a three site session type

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The session types Metro Mirror – Global Mirror, Metro Mirror – Global Mirror with Practice, and Metro Mirror – Global Mirror with three Site Global Mirror, now support the ability to convert from a multi-target configuration to a cascaded configuration and back. Cascaded configurations change the session so that the Global Mirror relationship is cascaded off of the Metro Mirror relationship and behave similar to the Metro Global Mirror session type.
When in a supported state, the Start H1->H2->H3 or Start H2->H1->H3 command is available which converts the session from a multi-targeted to cascaded configuration.
To convert from a cascaded configuration back to a multi-target configuration, the Start H1->H2 H1->H3, or Start H2->H1 H2->H3, command is available in supported states.

Before you begin

  1. Conversion between multi-target and cascaded modes, and vice versa, is done without a full copy. However, full three site protection is not available until the conversion is complete, so the change should be scheduled for an appropriate time.
    Note: If HyperSwap is enabled, during the conversion from multi-target to cascaded mode, HyperSwap is temporarily disabled at a point during the conversion to establish the pairs for cascaded incremental resync capabilities.
  2. The session must be in Suspended or Suspended Partial state to transition from multi-target to cascaded mode
    Note: The session does not need to be in suspended state to go from cascaded mode back to multi-target.
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  3. After recovering the session to H3, from being in a cascaded H1->H2->H3 or H2->H1->H3 mode. The options for starting at H3 are limited to commands which avoids a full copy.
  4. While running the session in the cascaded H1->H2->H3 or H2->H1->H3 mode, if the intermediate site is lost, an incremental start from the primary site to the remote site is available as it is in a Metro Global Mirror session.
    Note: In the event that a disaster occurs while in a two site Global Mirror configuration, after losing the intermediate site, any Start command from Site 3 results in a full copy of the remote Global Copy leg. This case is rare and occurs only after first losing the intermediate site and then the primary site.