In previous versions of vSphere, VMFS upgrade can only be performed form command line but vSphere5 have an in-build GUI option to upgrade to VMFS 5 version.Upgrading from VMFS 3 to VMFS 5 can be performed online with active VM’s running on it. I would always recommend to create a new Lun formatted with VMFS 5 and then migrate the VM’s from old datastore to new one.
Below is the steps
1.In vCenter server, select the Host->configuration -> Storage
2. Select the datastore which you want to upgrade it to VMFS5. Review the existing VMFS version.
3.Click on Upgrade to VMFS-5. All the hosts connected to datastore should be compatible with VMFS5 version.In otherowrds,Datastores are accessible to ESXi 5 hosts only.
4. It will take few seconds to minutes to convert to VMFS5 version.
5. Review the VMFS version now and It is converted to VMFS 5. VMFS file system version is now VMFS 5.54. Option to Migrate to VMFS-5 is disappeared now for the datatsore “ESXstorage3”.
Thanks for reading!!!!