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  • 1.  Global Mirror secondary be another Global Mirror primary

    Posted Wed January 15, 2025 02:57 AM

    Hello

    May I ask if the Global Mirror secondary volume can be another Global Mirror Primary ?

    Thanks.



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    Arthur Chang
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  • 2.  RE: Global Mirror secondary be another Global Mirror primary
    Best Answer

    Posted Wed January 15, 2025 04:45 AM

    This is possible but it only makes sense in specific scenarios.

    When the first Global Mirror relationship (A to B) is forming consistency groups then the second Global Mirror relationship (B to C) will not form any consistency groups and will simply be sending data with Global Copy.

    If you perform a consistent pause of the first Global Mirror relationship then when this relationship pauses (and the B device state changes to "consistent suspended" then the second Global Mirror relationship will now form consistency groups. 

    As you can see this scenario is not especially useful if both relationships are for disaster recovery but it can be helpful in the context of a Cyber Vault environment or datacenter migration. 

    btw - If you are an IBM employee then you might also want to consider using the #ds8000-help slack channel within IBM for these type of questions 



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    Nick Clayton
    STSM - Solution Architect for DS8000
    IBM
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    Original Message


  • 3.  RE: Global Mirror secondary be another Global Mirror primary

    Posted Thu January 16, 2025 09:18 AM

    When the A-B relationship is running the B-C relationship will be failing to form consistency groups - so effectively running in Global Copy



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    Nick Clayton
    STSM - Solution Architect for DS8000
    IBM
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    Original Message


  • 4.  RE: Global Mirror secondary be another Global Mirror primary

    Posted Fri January 17, 2025 11:23 AM

    Hi Nick, I came across this post and found it relevant to a DC migration project we've recently started.

    In our case the A-B relationship will be GM managed by CSM.

    The B-C relationship will be GM managed by GDPS.

    When A-B is actively forming CGs, I understand that B-C will be in Global copy mode until it is paused.  While in this state (B-C in Global copy), what will the state of the GDPS session be?  WE normally see a state of RUNNING on our GDPS-Global sessions but in this case will the state be sitting at CG-FAIL until we pause A-B?   



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    Phillip Allison
    Enterprise Architect
    ICE, Inc
    Jacksonville FL
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    Original Message


  • 5.  RE: Global Mirror secondary be another Global Mirror primary

    Posted Mon January 20, 2025 05:00 AM

    Hi Phil,

    The state will be CG Fail as the session will be trying to form consistency groups but failing because of the state of the primary (secondary device in duplex pending).

    Nick



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    Nick Clayton
    STSM - Solution Architect for DS8000
    IBM
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    Original Message