I've been doing this another way, not quite as the tool was intended, but for a reason. I wanted to be sure that, if my C: drive failed, I could replace it quickly with a complete backup that I could boot from and get running again. There also is a D: drive for additional data only (not bootable).
My external unit is a Seagate drive mounted in an Azio enclosure, and connected via eSATA. So I downloaded the Seagate utility Disk Wizard which appears to be a customized version of Acronis True Image. It includes a tool for drive cloning, which is what I use for this. But it is designed to make a clone TO only a Seagate HDD, so that's why I use it.
First, I use the utility to Delete any and all previous Partitions on the external drive. Then I clone my C: drive to the external unit. BUT I do NOT just accept its default settings. I use the menus to make the clone copy smaller than the original C: drive, but large enough to accept all its contents, and bootable. THEN I do a separate clone of the D: drive to that same external unit, doing a similar size adjustment, and putting that second clone image into the Unallocated Space left over from the first cloning operation. That clone does not need to be bootable. Now that external unit has TWO clone copies on it - one for each of my internal drives.
If I then look in My Computer, the C: and D: drives are there of course, plus identical versions of them under different letter names on the external unit. And all are accessible.
Now came the critical test. I disconnected my two internal HDD's. Then I removed the HDD unit from the external enclosure, mounted it inside my case and connected it up. I made sure that I connected its data cable to the SAME mobo SATA port as my original C: drive was on, just so the BIOS would have no difficulty finding the boot device. I powered on and sure enough, the machine booted from the first Partition of the (formerly external) HDD, and I had both C: and D: drives to work with containing all my data. Only difference was, the two drives each were a bit smaller than the originals.
Having proved it worked, I removed the "external" unit and re-mounted it in my enclosure, then reconnected my original two internal HDD's. Of course, the machine was back to normal, and I had my backups in the two Partitions of the external HDD unit.
I can wipe the HDD unit in the external enclosure any time ad re-make the two clones. And of course I keep it disconnected from the computer while not using it.
The major differences between what I do and a normal backup system are: (a) I don't make any incremental backups - only complete backups; and, (b) my backups are not in any proprietary file - they are just complete clones of my original drives, and I can use the HDD containing the clones to replace my original drives completely (allowing for size differences) so I can boot and run normally after a relatively simple hardware drive transplant, rather than a Restore operation using software. There's also the small factor that, for a short period of time while I delete all previous stuff on the external and re-make the two clones, I have no backups at all.