vSphere 5 introduced new file system version: VMFS-5. It brings a lot of improvements for scalability and performance (details can be found here) so if you haven’t done it already this is how you can upgrade your VMFS-3 datastores to VMFS-5.
The operation is non-disruptive for VMs hosted on the datastore but cannot be rolled back. To upgrade a datastore successfully, all hosts with access to this datastore must be ESXi 5.0 or higher.
Go to Hosts and Clusters inventory view, select a host that can access the datastore to be upgraded. Go to the Configuration tab and under Hardware select Storage. This will show all datastores the selected host has access to:
Select the VMFS-3 datastore. Below you will see a link Upgrade to VMFS-5. Click it.
A warning will appear confirming that all your hosts connected to the datastore must be in version 5. Click Ok.
That’s it. The datastore will be upgraded and you will be able to use new features such as GPT and uniformed block size.
What about block size and partition table on upgraded datastores?
When creating a VMFS-3 datastore you had an option to choose a block size for the new partition:
This is no longer an option as VMFS-5 uses only one, uniformed block size – 1 MB. However, when a VMFS-3 datastore is upgraded to VMFS-5, it will retain all partition characteristics with one exception: MBR will be converted (seamlessly) to GPT at the moment the datastore’s size exceeds 2TB.
The rest of the partition features will remain the same so VMware suggest temporarily moving the VMs with Storage VMotion to another datastore and recreating the empty one with VMFS-5 from the scratch.