Keeping data forever?
There are a few challenges:
Physical locations fail.
Media fails catastrophically (crashes). Try to keep it on two _different_ forms of media, at least one of which should not be vulnerable to shock.
Media fails slowly (bit rot). Try to use something that is resistant to this, something that can detect this, and something that can recover afterward.
Checksums and hashes (preferably SHA512 or another 512-bit current generation hash) for larger files... like databases can detect this; but don't resist and can't help you recover.
RAID1 and RAID10 is not necessarily a good choice; does your implementation correctly figure out which of two supposedly good copies that are somehow different is correct, assuming neither drive is reporting a bad block?
RAID5 and RAID6 fit all three criteria if and only if consistency checks are performed; without this, it's entirely possible for bit rot to be hidden until one (RAID5) or two (RAID6) drive fails, after which they cannot recover (and may not be able to detect).
Reed-solomon and other ECC software solutions (DVDisaster for CD, DVD, and Blu-Ray
, Par2+TBB for files in general
, etc.) can both detect and recover from bit rot or partial physical media destruction.
Means to read your media no longer exist. So; you've got some reel to reel tape, likely in EBCDIC, in the closet. You're going to read this how? Or a tape cartridge from the late 80's? 8" floppies? A stack of punch cards? Even if it is good (not terribly likely except for the punch cards, which are probably fine), do you have anything left that can read it? Do you have something to plug it in to? Can that something talk to anything else anymore, and if so, how close to modern tech can you get with each jump?
You need to keep moving the archived data onto newer media, and running some kind of bit rot check every time, making sure each copy really is accurate.
Catalogs are forgotten. A much harder problem; after twenty years, if there's no one left that remembers either what file X is, or how to answer question Y... what good are your forever archives, particularly if you have eight versions of almost the same thing?