ODX just accelerates your data transfer whereas VAAI does the below: Atomic Test & Set (ATS), which is used during creation and locking of files on the VMFS volume Clone Blocks/Full Copy/XCOPY, which is used to copy or migrate data within the same physical array Zero Blocks/Write Same, which is used to zero-out disk regions Thin Provisioning in ESXi 5.x and later hosts, which allows the ESXi host to tell the array when the space previously occupied by a virtual machine (whether it is deleted or migrated to another datastore) can be reclaimed on thin provisioned LUNs. Block Delete in ESXi 5.x and later hosts, which allows for space to be reclaimed using the SCSI UNMAP feature. For more information on Block Delete/SCSI UNMAP
