[Asbostos]

Surely it's OK for a backup drive to fail occasionally. Your working drive might fail occasionally too but it's extremely unlikely that both of them fail within a day or so of each other. That's the situation that would lead to loss of data.

That's for a pure backup. For a history of previous versions, of course you'd want more reliability if you only have one copy of that history.

[quanticle]

I think the concern here is that the backup drive could have silently failed at some point in the past, corrupting the backups, and then the primary would fail too, leaving you without any backups whatsoever.

[ioquatix]

When you only have a master and backup drive, in the case of failure, you put yourself in a critically dangerous position.

Restoring from backup isn't just stressful for the human, it's also stressful for the hardware.

When you have a single failure, it's nice to at least have TWO independent backups in case during the restore there is a second failure (either due to hardware or operator).