Ever since ESX3.0 we have used the VMFS3 filesystem and we are still using it on vSphere. What most people don’t know is that there actually is sub versions of the VMFS.

        ESX 3.0 VMFS 3.21
        ESX 3.5 VMFS 3.31 key new feature: optimistic locking
        ESX 4.0 VMFS 3.33 key new feature: optimistic IO

 The good thing about it is that you can use all features on all versions. In ESX4 thin provisioning was introduced but it does need the VMFS to be 3.33. It will still work on 3.21. The changes in the VMFS is primarily regarding the handling of SCSI reservations. SCSI reservations happens a lot of times. Creation of new vm, growing a snapshot delta file or growing thin provisioned disk etc.

I want to make sure everyone realizes that this is actually not true. All the enhancements made in 3.5, 4.0 and even 4.1 are not implemented on a filesystem level but rather on a VMFS Driver level or through the addition of specific filters or even a new data mover.