Is vSAN able to return disk space to a repository when deleting files in the guest OS of a virtual machine? The answer is not yet, but they are working on it.
If we take a virtual machine in a vSAN cluster with a guest OS of Windows Server 2012 R2 with 386.7 GB of occupied space (the VM itself was deployed on thin disks):
Copy 800 MB there after which we can see that the occupied space had increased to 388.37 GB, that is, it grew by 1.6 GB. This is logical, since vSAN worked in RAID-1 mode (mirrored VMDK disks):
Delete the newly copied files and made sure that the occupied disk space was the same (that is, there is no UNMAP / TRIM support inside the guest system in vSAN):
Meanwhile, copy the same 800 MB and notice that the disk space increased by only 20 MB (in total, 40 MB with RAID-1 in mind).
That is, the blocks occupied after the last copy were reused:
Such a thing is in Windows Server, but Linux does not perform such a trick on the ext4 file system. Anyway, when you copy the blocks again, the blocks will be located elsewhere, and the space will be reused. For ext3 and XFS the blocks will also be reused.
Well, remember that this is only applicable for deleting files from inside the guest OS, if you delete a virtual machine or another object on the vSAN storage, the space will immediately return to the shared storage pool.