backup disk formatting

[Dan Lester]

Just an FYI, not sure if it's been talked about before. I was trying to create a bootable backup for an old machine, for which the internal disk was formatted MacOS Extended (Journaled). The backup was accidentally done on an SSD that had been formatted with the modern APFS. When the backup was done, I did option-restart to get the Mac Boot Manager, and the backup disk DIDN'T APPEAR! When I did it again after reverting the backup disk to MacOS Extended (Journaled), everything worked dandy. Make sure your backup disk is formatted the same way as the disk you're backing up! Now, of course, older Macs can't read APFS, but you'd think that when SuperDuper is making a backup to a disk that isn't formatted in a compatible way, it would complain.

[dnanian]

If the OS supports APFS, we're happy to copy to APFS. Anything on 10.13 or later should be able to boot from APFS as well...unless that Mac has never had its firmware updated to add the support.

[Dan Lester]

Thanks. Not a big deal, but if the OS DOESN'T support APFS, it strikes me as a little funny that SuperDuper blasts ahead with trying to copy to a non-APFS disk. That is, you only find out half an hour later, when the copy you tried to make doesn't boot because, I guess, it isn't really there.

[dnanian]

If the OS doesn't support APFS, we would copy to a non-APFS disk...? And if the OS doesn't support APFS (eg 10.12) we won't.

If the firmware hasn't been updated for boot-time APFS support, we don't know - that capability isn't exposed. But installing the OS (rather then restoring) will ensure that the firmware is updated...these things are distributed with installers.

[Dan Lester]

Sorry, not being clear here. If you connect an APFS disk to an OS that does not know how to communicate with APFS, SuperDuper will STILL try to copy, and takes time grinding away seeming to do it. But what you end up with, after a long wait, is a disk that won't boot, and probably doesn't even have a copy on it. My point is that SuperDuper doesn't seem to recognize that it's trying to copy to a disk that the OS formally can't communicate with, and you don't find out until the disk doesn't work. Are you saying that SuperDuper has no way of polling the disk to see if it is really writable?

[dnanian]

No, Dan, it won't. If the system does not know how to communicate with APFS, the drive won't even mount.