I was just answering some questions on the VMTN forum when someone asked the following question:
Should I upgrade our VMFS luns from 3.21 (some in 3.31) to 3.46 ? What benefits will we get?
This person was referred to an article by Frank Brix Pedersen who states the following:
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 datamover.
Just to give an extreme example: You can leverage VAAI capabilities on a VMFS volume with VMFS filesystem version 3.21, however in order to invoke VAAI you will need the VMFS 3.46 driver. In other words, a migration to a new datastore is not required to leverage new features!