Thanks for your confirmation that what you see in MSA exactly matching in ESX as well. So one part is done - this means both system base value set at correct value.
Now you need to understand what is Thin Provision volume that will clear all your doubts.
In MSA no one is stopping you to create third volume and that is not related or depend on how much unallocated space you have in the system.
You can create even 30TB volume with current condition eventhough you don't have that much space available in the system. This is the beauty of Thing provisioning. This means you have created 30TB provisioned volume - this means your volume can take space up to 30TB that doesn't mean you need 30TB space at the time of creation itself. In order to create a thin provison volume you just need some KB of size only. As in when you start writing data on it at the host filesystem level space will get allocated for that volume from Pool from which it got created at the backend.
Now anothing thing to make you understand, for any volume allocated space and unallocated space are committed space for that volume from the Pool from which it got created. This means if you have created 30TB volume then this is expected from that pool that it should be able to provide 30TB space to that volume. So Pool is committed to provide this much space to the volume. That's why unallocated space even though not yet allocated to the volume but this space committed to that volume.
Now any space which shows under uncommitted means this space part of the Pool but not required to be for any volume as unallocated space fullfil the requirement of committed space. Both uncommited space and unallocated space represents free space in the Pool.
So in your case if you really create any third volume with current condition and plan to use it then you can do so but make sure you closely monitor them and add more space to fulfill all volume commited space requirement.
In ESX if you see any MSA volume space.......this can't be fixed.......it must change........you can clearly see it...........you may be looking at the datastore screen only...........you need to explore more to see it properly
Hope this helps!
Regards
Subhajit
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