System backup to another drive

[Tyrannocaster]

I have an SSD as a system drive, and I have two internal conventional disks as well, both formatted FAT-32. I'd like to backup my system to one of the bigger drives, but Timeshift tells me it can't do that. Timeshift also tells me my SSD is not a Linux formatted device, though, which is obviously incorrect. Despite that message it does appear to backup the system to the SSD, but AFAIC that's of limited value since if the disk dies, so does the backup.

Any ideas welcome.