Well, I've worked for 1 year at HP phone support, especially on tapes.

I assure you that tapes fail all the time. Their mechanical nature and the strain on their delicate components make them susceptible to failure.

EDIT: Unless you're talking about high end like Ultrium. In that case, it's solid. But then much slower, more expensive than a same size hard drive.

Most of my experience has been with Ultrium TBH. But you can pick up Ultrium 1.5TB tapes for less than the cost of a equivalent sized hard drive, here in the UK at least.

That's because disks are expensive in the UK, not because tape is cheap.

You can get 2TB of disk storage for <$100 in the US when you are buying retail (if you buy three hundreds like this guy needs, you'll probably be able to get it down to $30 or $40 per TB).

No tape device required, comparable speed, disks are random access; A backblaze-style setup in todays costs sets you back ~$60/TB for online, random access, storage redundancy and other nice things - 500TB can be build for $30K or so, with a few hundred dollars/month for electricity (and a few hundreds more for colocation if you don't have the office space).

How cheap can you get a functioning system with reasonable (a few minutes) retrieval time when you have 400 1.5TB tapes? (you need redundancy here too, you know).

Since sometime in '98, tapes make no economical sense whatsoever for any kind of storage, and hardly any sense at all, as far as I can tell.