In general whatever space you see as Allocated in MSA that means data written in that space in Pool level or VDG level but the space shows as Unallocated means volume not yet written data in it. So unallocated space related to volume level
If I take your example, in case of Pool A total size = 13.1TB
Provisioned size of volume named v04_10TB = 13.1TB
Allocated size of v04_10TB = 9.3TB
This means unallocated size at the volume level = (13.1-9.3)TB = 3.8TB [This space not dedicated for any particular volume, this can be use by any volume part of that Pool]
I understand you have expanded volume size but the host side your host operating system support online volume expansion at the file system level? if not then I would suggest you to unmap the volume and remap the volume to host to get the expanded provisioned size of the volume
Hope this helps!
Regards
Subhajit
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