Thanks for getting back to me. Yes, the drive has multiple partitions; I haven't tried booting with only one but even if it did work I wouldn't keep this drive because it's 4TB and my clone is only around 250GB at most, I got the larger one to be able to do Time Machine backups of my Mac and the household laptops too. (Am I correct in assuming that the TM backups have to be in a separate partition from the SuperDuper clone or else they'll be erased?)

And yes, it is partitioned as GUID.

No, as I explain in the FAQ entry, they can share the same volume as long as you use Smart Update...but TM does grow until the drive is full, so eventually you'll fail.

Some Macs have problems with large (>2TB) drives if the partition you're trying to boot from is past the 2TB "point" on the drive...

Sorry, missed that, I'll have a go at putting them in the same partition.

Could you explain what you mean by "past the 2TB point" - do you mean larger than 2TB or lower in the list after a 2TB+ partition (ie does the order of creating the partitions matter)?

Thanks

Yes, the order matters. The boot volume needs to be in the first 2TB.

Yeah, success, thank you!! It didn't work combining TM backups and SD backups in one partition but once I erased the disk and made the SD partition the top one everything was fine.

But one more silly question, sorry - if I want to do SD backups of additional computers, those need to be in separate partitions, correct? Ie even Smart Update of a second Mac would overwrite the first Mac's clone?

Thanks again

Yes, they'd have to be separate volumes.