This morning when turning on a Mac laptop, it suddenly announced that an external backup disk (which was connected overnight) "can't be repaired". Disk Utility also says:
Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.
The volume can't be mounted at all.
How can I diagnose if this failure is due to hardware problem or if it's entirely a software problem? Is it for example possible to have Disk Utility look for bad sectors? The same disk has another (exFAT) partition which seems fine.
I need to know if the whole disk is bad, and needs to be replaced, or if it's safe to use after reformatting.
The disk has never been subjected to mechanical stress (it wasn't even carried much), so I suspect it might not be a hardware failure.