> but with HDDs you must take care to always use both duplicate HDDs and archive files with redundancy

I'm a noob when it comes to tape backups. Is copying the same stuff to multiple tapes standard practice?

> There is also the problem that the availability in the future of Blu-ray recorders and readers is uncertain.

LTO drives used to read tapes from 2 generations back, then just 1. LTO 10 isn't backwards compatible. Future availability of compatible tape drives is also uncertain.