Imagine putting a git-annex drive in a time capsule. In 20, or 50, or 100
years, you'd like its contents to be as accessible as possible to whoever
digs it up.

This is a hard problem. git-annex cannot completely solve it, but it does
its best to not contribute to the problem. Here are some aspects of the
problem:

* How are files accessed? Git-annex carefully adds minimal complexity
  to access files in a repository. Nothing needs to be done to extract
  files from the repository; they are there on disk in the usual way,
  with just some symlinks pointing at the annexed file contents.
  Neither git-annex nor git is needed to get at the file contents.
  
  (Also, git-annex provides an "uninit" command that moves everything out
  of the annex, if you should ever want to stop using it.)

* What file formats are used? Will they still be readable? To deal with
  this, it's best to stick to plain text files, and the most common
  image, sound, etc formats. Consider storing the same content in multiple
  formats.

* What filesystem is used on the drive? Will that filesystem still be
  available? Whatever you choose to use, git-annex can put files on it.
  Even if you choose (ugh) FAT.

* What is the hardware interface of the drive? Will hardware still exist
  to talk to it?

* What if some of the data is damaged? git-annex facilitates storing a
  configurable number of [[copies]] of the file contents. The metadata
  about your files is stored in git, and so every clone of the repository
  means another copy of that is stored. Also, git-annex uses filenames
  for the data that encode everything needed to match it back to the
  metadata. So if a filesystem is badly corrupted and all your annexed
  files end up in `lost+found`, they can easily be lifted back out into
  another clone of the repository. Even if the filenames are lost,
  it's possible to [[tips/recover_data_from_lost+found]].

* What about upgrades to the git-annex repository format?
  git-annex supports [[upgrades]] from all previous repository versions,
  and will always support upgrading from all of them to any new versions.
  Note that the upgrade process needs to modify the content of the
  repository -- if modifying the original archived repository is not
  desirable you can always make a copy of the repository and upgrade the
  copy.

* What about encrypted special remotes? A 
  [[fairly simple shell script using standard tools|tips/Decrypting_files_in_special_remotes_without_git-annex]]
  (gpg and openssl) can decrypt files stored on such
  a remote, as long as you have access to the encryption keys (which
  for some types of encryption are stored in the git-annex branch of
  the repository, sometimes encrypted with your gpg key).