Repository backups

I'd like to build a modest safety net for my various git repositories in case of catastrophic failure. Currently, everything is backed up on machines in the same building. I'm not expecting the Computer Science building to get hit by terrorists and we're in a seismically stable place, but there *is* construction nearby...

Anyway, my university offers a "mass storage" tape-based service that is supposedly very safe. We are encouraged to give them single big files for backups.

The temptation to just make bundles of all branch heads is great but probably not what I really want - things like reflogs don't get handed off with those, if I understand correctly.

Is there any argument against just making a tar of a bare clone of the repo? Any other ideas? I'm reluctant to actually clone into the tape (SAM-FS, which I know nothing about) because of the number of files it would create and the lack of git tools on the machines with access to this machine.

Thanks, Jason