Tape + Iron Mountain is difficult to beat for offline copies.

Surrendering just a little bit of absolute control over the physical media can dramatically increase the likelihood that it survives whatever apocalyptic event. I don't know that I've ever heard of tapes being stolen from Iron Mountain. Even if this happened, what are the odds that they would get all the tapes. Your tapes? It probably looks like the warehouse from Raiders of the Lost Ark in there.