Actually... when you use archival quality media, Blu-Ray discs will survive about 10-20 times longer than an average HDD or Flash Media device. HDDs and Flash Media are Not Recommended for Archival level storage.
Theoretically, sure. But those discs are more expensive than the $8-10 per 50GB price I mentioned. Also, there's another issue that people don't tend to think about when they discuss those long-term backup storage concerns. (It's one that NASA has actually run into.)
All but the worst HDD or flash drives will last more than 2-3 years (low-ball estimate), even sitting somewhere safe 'collecting dust'. Even with archival quality Blu-Rays, however, the life-time estimates are just that, estimates based on best-possible storage conditions. For the rest of my post here, I'll assume that they actually live up to their claims in order to demonstrate just how little that will likely mean in the long term.
Take that out to 10-20 times longer, and you're looking at 20-60 years. What was the back-up medium 10 years ago? Tape. What was the back-up medium 60 years ago? Paper.
Find me a tape drive which you can install in your current system that supports a 20 year-old tape format. If you're *lucky*, you'll find an internal port which ran off a floppy port, and be able to find a floppy-to-USB adapter that you can scavenge from an old USB floppy drive. Then you'll run into the issue of finding drivers to let your computer use the device.
Do you expect to be able to find a Blu-Ray compatible drive 20+ years from now? If you can, do you expect your computer then to have drivers to support it?
The unmentioned fact of the matter is that, with the way computer technology changes, a 10 year-old backup is very likely to be absolutely useless to someone even if the media itself is still readable. If you really want long-term backups, you're going to be dependent upon being able to transfer your old backups to modern media periodically.
With the way prices for storage drop, doing this is going to mean buying your backup media based primarily upon storage capacity and read/write speed, and physical storage constraints. Blu-Ray isn't currently superior to *any* of the other common options these days in those categories.
For example, a 3TB desktop HDD takes up significantly less space and is significantly faster than the 60 Blu-Ray disks it would take to store the same amount of data. Additionally, the 3TB drive is significantly less expensive and requires less manual intervention to use. In 10 years when it's getting harder to find SATA equipment than it is to find whatever the newer replacement is, you'll likely be able to transfer all your 3TB backup HDDs onto a single unit of newer storage.
