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remote copy group and copy cpg
https://3parug.com/viewtopic.php?f=18&t=3214
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Author:  pazzoide76 [ Tue Jun 11, 2019 2:35 am ]
Post subject:  remote copy group and copy cpg

Hello everyone,
I have to put in periodic async replication two 3par.
I have a question asking about remote copy groups and copy cpg.
When I create a virtual volume I have to configure the user cpg and the copy cpg.
When I create a remote copy group also in this case I am asked to configure a copy cpg.
So am I creating a remote copy group in periodic async mode to take snapshots which cpg copy group is used?
So to make the snapshots needed for replication, 3par uses the cpg that I configured when I created the virtual volume or 3par uses the cpg that I configured when I created the remote copy group? Or does 3par use both cpg copy?

Thank you

Greetings

Author:  ailean [ Tue Jun 11, 2019 5:00 am ]
Post subject:  Re: remote copy group and copy cpg

It would probably depend on which array held the active volume, the copy of the volume that is being used by the host will be the one holding the snapshots for replication. Once the data is sent to the target array the snap can be released. If you fail the volume to the other array for DR then you'd reverse the replication and snaps will be on the target until they can be sent to the original array.

You can set all the CPG values to point to the same CPG (on each array), the separate option is normally if you have tiers and want the snaps to live on 'cheaper' disk (not that any 3PAR disk is cheap :) ).

Author:  pazzoide76 [ Tue Jun 11, 2019 7:38 am ]
Post subject:  Re: remote copy group and copy cpg

Thanks for the reply.
At this point I didn't understand if the cpg defined in the remote copy group or not is used for snapshots concerning remote copy.
I need to understand if only the cpg I defined in the remote copy group is used or not.
In my case I have a cpg in raid 5 (4 + 1), with fc 15k disks, and the copy cpg point to itself.
I created a remote copy group and made the copy cpg point to a raid 6 cpg (4 + 2) raid with fc 10k disks.
In my case, which copy cpg is used for remote copy?

Thank you

regards

Author:  ailean [ Tue Jun 11, 2019 8:01 am ]
Post subject:  Re: remote copy group and copy cpg

I've always set the rcopy groups to match the VVs being added, CPG wise, I'm sure I've seen an error when one didn't match but been a while (might just be the user CPG). The remote/target CPG settings I think were added to support the automatic creation of target VVs with the VMware plugins (the settings didn't exist before that from what I remember).
We've not had tiers in a 3PAR for 5+ years so had little need to mix CPGs and we don't have snaps around for long so wasn't a priority where they were stored.
Sorry you might need to experiment unless someone else has mixed settings and can share. ;)

Author:  MammaGutt [ Tue Jun 11, 2019 9:29 am ]
Post subject:  Re: remote copy group and copy cpg

There is only one copy cpg per volume. When you create a volume on 3PAR-1 you configure the user and copy CPG on 3PAR-1. When you configure Remote copy group you configure user and copy CPG on 3PAR-2.

You never want your snap to be on the cheapest disk.... In a multi-tier config you usually put copy cpg on FC. Putting it on NL might crush your NL tier when it comes time to push that snapshot to the other 3PAR. There are also other similar scenarios as well.

if you have dedupe enabled, it can in some cases be very smart to keep user and copy as the same cpg.

Author:  pazzoide76 [ Wed Jun 12, 2019 2:31 am ]
Post subject:  Re: remote copy group and copy cpg

Thanks for the reply.
From what I have understood, the cpg copy that is set during the creation of a remote group only serves to create new virtual volumes.
The existing vitual volumes take the cpg copy space from the virtual volume setting

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