VMware vSphere 4 Essentials Plus licence does not include SCSI Hot-Add. The SCSI Hot-Add feature in vSphere allows one virtual machine running a backup application to mount the disk of another so it can read the data from it and write it to destination media. Doing this removes the backup traffic from the network as the VM running the backup application uses the VDDK to access the disk and all I/O requests to it are sent directly down the VMkernel I/O path
