1st of all it depends upon what type of volume created on ESX. It means Thin, Thick Lazy Zeroed and Thick Eager Zeroed.
If you concern about space reclaim then UNMAP comes into picture for Thing provisioned volume only where after deletion of data or complete VMDK file ESX need to tell MSA that you also reclaim physical space now. This is extremely slow process as MSA Page size only 4MB. You can check live data from MSA CLI by running below command,
show disk-group-statistics
From the above command output you can see columns "Pages Reclaimed" and "Pages Unmapped per Minute".
You can check the below article to get some idea how space reclaim works with the use of unmap command in Vmware,
https://kb.vmware.com/s/article/2057513
In case of Thick all space already Zeroed out so from MSA perspective it's always occupied space. Now in VMFS level whatever you are doing doesn't matter for MSA.
Hope this helps!
Regards
Subhajit
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