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 Post subject: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Thu Jun 25, 2020 8:42 am 
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Joined: Mon Mar 02, 2020 11:07 am
Posts: 3
Dear all,

I am looking at the used and reserved sizes of some virtual volumes. We managed two 3PARs and have Remote Copy Groups copying the data/vvols between them.

I have one vvol where on the Primary 3PAR it's reserved size is 750GB
but on the secondary 3PAR it's reserved size is 2.4TB (three times larger)

Since the vvol on the secondary 3PAR is just a copy I would have expected it to be exactly the same size.

What can I do to fix this and get the space back. My only guess would be to stop and delete the remote copy group. Delete the vvol from the secondary 3PAR. The recreate the remote copy group and have it re-sync the vvol all over again.

Any help is gratefully appreciated.


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 Post subject: Re: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Thu Jun 25, 2020 9:09 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1124
Location: Europe
Little bit more info please.

Usr Used should be close to equal on both sides. Reserved depends on a lot of factors so they usually aren't. If you have sync replication and PP you could try a switchover to see if reclaim improves.

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 Post subject: Re: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Thu Jun 25, 2020 10:15 am 
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Joined: Mon Mar 02, 2020 11:07 am
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Yes, the User used space is the same (700GB) on both 3PARs.

We do have Peer Persistence so I could try a switchover. I came still unsure why the reserved space reclamation would be so different.


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 Post subject: Re: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Thu Jun 25, 2020 11:54 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1124
Location: Europe
Mark.Bell wrote:
Yes, the User used space is the same (700GB) on both 3PARs.

We do have Peer Persistence so I could try a switchover. I came still unsure why the reserved space reclamation would be so different.

Even if they are the same volume, they are on two different arrays, in two different CPGs using different LDs. Also the characteristics of the volumes are totally different where one is 100% write and the other usually read heavy.

There has also been a few features over they years that made reclaim stop for some volumes, but doing a switchover should show if that's the case pretty soon.

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 Post subject: Re: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Wed Jul 15, 2020 3:48 pm 

Joined: Sat Nov 24, 2018 4:18 pm
Posts: 23
Hello, from my experience, when I was playing with scsi discards, I triggered reclaim by running a compact_cpg task. This is not running by default, so I scheduled them.


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 Post subject: Re: Two Vvols in a Remote Copy Group different Reserved size
PostPosted: Wed Jul 15, 2020 4:06 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1124
Location: Europe
feldsam wrote:
Hello, from my experience, when I was playing with scsi discards, I triggered reclaim by running a compact_cpg task. This is not running by default, so I scheduled them.

In that case you got it all wrong.

Compact cpg releases free capacity from the CPG to the system.
Reclaim releases free capacity from the volumes to the CPGs.

Reclaim is running as a hidden task triggered every five minutes on a limited amount of volumes (I think 8)each run. If reclaim "fails" (ie it can't reclaim anything from a volume) and the volume has more than 4GB of free capacity per node in the system it will trigger a defrag task on the volume (visible).

Compact CPG is usually a manual task. The only way I know it autotriggers is if you're doing AO and hits certain parameters. In most cases compact cpg isn't really needed. Remember that the CPG will use the free capacity in the CPG before allocating new capacity. So in most cases where you are expecting the CPG to grow at some point and you're not low on capacity with multiple CPGs on the same tier, compact cpg is simplity wasted IOs.

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