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Virtual Volume across 2 CPG's

 
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Victor G
Advisor

Virtual Volume across 2 CPG's

Hi,

I have a virtual volume which has been configured across 2 CPG's. CPG1 consists of SSD disks and CPG2 consists of FC disks.

In the past I think that we the VV ran out of space on the CPG1 ( SSD ) so another was somehow added using CPG2 ( FC disks ) and the volume extended.

Virtual Volume.JPG

I didn't think this could be done and that there was a 1:1 relationship between an VV and CPG.

I have been increasing space of the VV and I believe it has been taking space from the FC CPG, but I don't understand how this is defined.

Can anyone enlighten me on how this has been achieved ?

Thanks,

Victor

3 REPLIES 3
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Re: Virtual Volume across 2 CPG's

You have created VV initially based on one CPG which is SSD CPG. Later you faced situation like running out of space for SSD drives and then you have added FC drives and created FC CPG. In this situation when new write comes to that VV and it's not able to find space on SSD CPG then system automatically look for other CPG different drive type(in this case FC) and create LDs accordingly and allocate space there to accomodate that write request. That is how same VV data can be distributed among SSD and FC CPG.  Also if you have Adaptive Optimization (AO) configured then also you can see same VV data distributed among both CPG. To know exact details you can check below commands,

showvv -cpgalloc 

showvvcpg

 

Hope this helps!
Regards
Subhajit

I am an HPE employee

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Victor G
Advisor

Re: Virtual Volume across 2 CPG's

Hi Subhajit,

Thanks for you reply.

Can you tell me a what percentage of SSD disk full would the VV start to use the second CPG.

Also is there a way of manually forcing this, or is it always an automatic thing ?

Victor

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Re: Virtual Volume across 2 CPG's

It's based on CPG parameter configured and condition applied on SSD CPG. System will try to create LDs based on SSD CPG parameter configured and if system found that not sufficient space available to create LDs then it will automatically look for other CPG to create the LD.

Manually we can't control it because you never know when an IO may come and if LD need to be created for the same.

 

Hope this helps!
Regards
Subhajit

I am an HPE employee

If you feel this was helpful please click the KUDOS! thumb below!

***************************************************************************


I work for HPE
Accept or Kudo