You wouldn't usually backup the whole thing first. That 1 PB is probably a bunch of smaller projects, so you'd create a tar of the first project, then flush it to tape. Tar up the second project, then flush it to tape.
It's not so bad if you're writing 23 tarballs out to tape and pausing between each one. What you really want to avoid is where the tape drive is pausing many times during a single archive, perhaps because tar can't keep the drive fed while it's traversing a big directory of teensy files.
It's not so bad if you're writing 23 tarballs out to tape and pausing between each one. What you really want to avoid is where the tape drive is pausing many times during a single archive, perhaps because tar can't keep the drive fed while it's traversing a big directory of teensy files.