[elehack]

Backblaze can back up arbitrarily large local drives, but does not allow you to set network drives as backup sources (for precisely this reason). It's fine with the local drive being shared - our desktop's big storage drive is exposed over the network - but it can detect and refuse mounts from other machines. I don't know what it does with an iSCSI drive, haven't tried.

I think it's harder to detect network mounts in a way that wouldn't have a bunch of false positives on Linux.