Let me explain the MSA architecture.
Collection of physical drives made VDG.
Then VDG gets added to Pool A or Pool B
After that you create Volume from Pool A or Pool B
This Volume actually holds all VMs at the host side. So it doesn't matter this Volume got space from which VDG. In a Pool it can be multiple VDG possible and space can get allocate from any VDG. This is MSA Virtualization unlike linear array where you know which physical disk responsible for which Vdisk so you know volume gets space from which disk drive.
My suggestion will be if you want to increase size of the Pool and planning to create new VDG then always try to create VDG with same number of drives, same type drives, and same size drives. Also try to keep RAID level also same for all same tier drives VDG. This will help to increase performance of the system.
One Pool can contain different drive type VDG as well. Like there can be FC VDG, SSD VDG and NL VDG.
Hope this helps!
Regards
Subhajit
I am an HPE employee
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