* Don’t use ANY NAS/RAID technology. If anything goes wrong, your data is scattered in some proprietary format across umpteen drives and no-one is going to be able to piece it back together for you. Every RAID/NAS you buy is using its own custom sector layout format, if not its own custom filesystem and is totally useless without the controller. Stay far away from any device with LACIE written on it.
* Online/cloud. These companies GO OUT OF BUSINESS. Literally, one day you’ll see a notice that they are gone. You may get enough notice to get everything back, or not. Or you switch credit cards, forget to change the account, and poof, everything is gone.
* Don’t use tape: I performed the role the tech person in an intellectual property discovery case a few years ago and we had boxes of backup tapes. You would not believe how hard it is to successfully read tapes more than about 5 years old. Not only are the drives impossible to find, but the new drives can’t drop down to the lower data capacity, or they will eat the frigging tapes, or worse, break them.
If you are going for more than 5 years:
* Optical is possibly OK. The dyes that they use in optical media go bad. You have to carefully research the longevity of the dyes and you should probably be making multiple copies using media from different produced by different firms (guarding against a bad batch of dye). I am extremely skeptical of bluray right now. I have quite a few CDRs from 10+ years ago that are still readable.
* Flash: Flash technology works by charging a memory cell that is surrounded by an insulator. The charge eventually drains out. They say this takes 20 years, I would assume this is optimistic. The 1-bit-per-cell technology is more stable than the 2-bits-per-cell (I don’t remember the terminology, but you can tell by the performance which is which).
* Hard drives: Any *individual* IDE/SATA/SCSI/USB hard drive will be readable in the long term, provided the drive itself does not die. I put my offline content on multiple, individual hard drives (no RAIDs). For offline storage, RAID is a disaster waiting to happen.
If I had pictures I wanted to ensure I did not lose over decades, I would *print* them. Seriously.
