Re: Not a problem
"Where I work we're on an 11 year retention policy for every single piece of data. We have data stored on DDS DAT tapes, some of it is so old and has been deemed applicable to audit and must be kept."
I see this kind of misinterpretation of "kept" all the time.
Keeping the data is not the same as keeping the media. Migrating backed up data to new media is critical to ensure that your backups actually remain accessible.
If someone had to go find a drive on Ebay, that's prima-facie evidence that you haven't bothered actually periodically checking the integrity of those backups - which is a necessary requirement for any properly working backup system. As such the system should have a big red FAIL stamped on it.
Two worst cases I can think of off the top of my head:
1: The BBC micro and their Domesday book.
2: The academic I work with who has a garage full of 1970s-era NASA 9-track tapes full of raw data from earth observation satellites he wants restored one day - for shits and giggles I found an outfit which can do it. They want over £250 per tape - not "because they can", but because the equipment is so fragile (and head wear such an issue) that it costs about that much just to keep it running (people scrounging old electronics to find working bits have to be paid)
When I told him how much it'll cost, it put a dampener on his restoration plans. He'll never afford to be able to do it but he won't admit defeat and bin the tapes either. Every year he delays his decision the per-tape cost continues to climb and one day they won't be able to be restored at all (My suspicion is that the original data is still online inside NASA somewhere anyway, they seldom discard things)