> Just use a magnetic hard disk and your data will be fine for many decades if not centuries.

A few months ago I needed to pull from an offline backup. The disk, which used CMR and was purchased new from an actual computer supply company (i.e. not Amazon), was burnt in for about 72 hours before it was loaded up with data and shoved in a padded box. Ten years later, the drive was pulled, and there were so many media surface errors that most of the data was unrecoverable. (I haven’t bothered opening the drive to see if there is some obvious sign of what exactly failed.)

In my case the backups were created in multiples using two different brands for exactly this reason, and the second copy was fine. But I wouldn’t say it’s the case a single magnetic disk can take the place of BD.

Mechanical disks are also getting expensive. The disk purchased to replace the failed backup was being sold at three times its original release MSRP. Some of this is due to the AI hysteria but some of it is also that the market is shrinking and becoming K-shaped.