1. Ensure the datastore disks are presented to your Windows Backup host
2. Set your SAN policy to OnlineAll and clear the readonly attribute for each Datastore disk presented to the Backup host
diskpart >list disk
diskpart >select disk <x>
diskpart >attributes disk clear readonly.
diskpart >online disk
3. Make sure the Backup host has communication to the ESXi throught port 902, ex: telnet <esxi_hostname> 902
The reason why this is needed is because Metadata write is not supported for HotAdd and SAN transport.
When a program calls VixDiskLib_WriteMetadata with HotAdd or SAN transport, the function returns an error saying “The operation is not supported” and supplied metadata never gets written to virtual disk. The workaround is to close the disk from HotAdd or SAN mode, reopen the disk using NBD or NBDSSL mode, then call VixDiskLib_WriteMetadata.
For more information:
https://www.vmware.com/support/developer/vddk/vddk-601-releasenotes.html