The idea behind having two copies on tape is that it’s an easy way to get redundancy without special software. This makes it comparable to Backblaze, which presumably uses erasure codes, which allows them to achieve better redundancy with lower overhead (Backblaze’s storage can survive a higher rate of failure, and the encoding requires less overhead than a second whole copy).
What would be unfair is comparing Backblaze against a single tape copy.
However, two copies on tape is a pretty good backup. Paranoid, even.
Having had to restore from tape in very stressful circumstances, if I still did sys admin on that sort of thing I would definitely be paranoid enough to want a second tape off-site. If not daily, then at least on some sort of regular rotation. Though it would depend on the criticality, and for anything really critical I'd want a colo storage server as well. If the data is critical then even for a relatively small business $15k in upfront costs for the tape drives and lots of tapes and annual costs at the colo center wouldn't be all that much.
The idea behind having two copies on tape is that it’s an easy way to get redundancy without special software. This makes it comparable to Backblaze, which presumably uses erasure codes, which allows them to achieve better redundancy with lower overhead (Backblaze’s storage can survive a higher rate of failure, and the encoding requires less overhead than a second whole copy).
What would be unfair is comparing Backblaze against a single tape copy.
However, two copies on tape is a pretty good backup. Paranoid, even.