Amazon Glacier provides low-cost storage, well suited for archiving and backup. But it takes around 4 hours to get content out of Glacier.

Recent versions of git-annex support Glacier. To use it, you need to have glacier-cli installed.

First, export your Amazon AWS credentials:

    # export AWS_ACCESS_KEY_ID="08TJMT99S3511WOZEP91"
    # export AWS_SECRET_ACCESS_KEY="s3kr1t"

Now, create a gpg key, if you don't already have one. This will be used to encrypt everything stored in Glacier, for your privacy. Once you have a gpg key, run gpg --list-secret-keys to look up its key id, something like "2512E3C7"

Next, create the Glacier remote.

# git annex initremote glacier type=glacier keyid=2512E3C7
initremote glacier (encryption setup with gpg key C910D9222512E3C7) (gpg) ok

The configuration for the Glacier remote is stored in git. So to make another repository use the same Glacier remote is easy:

    # cd /media/usb/annex
    # git pull laptop
    # git annex enableremote glacier
    initremote glacier (gpg) ok

Now the remote can be used like any other remote.

    # git annex move my_cool_big_file --to glacier
    copy my_cool_big_file (gpg) (checking glacier...) (to glacier...) ok

But, when you try to get a file out of Glacier, it'll queue a retrieval job:

# git annex get my_cool_big_file
get my_cool_big_file (from glacier...) (gpg)
glacier: queued retrieval job for archive 'GPGHMACSHA1--862afd4e67e3946587a9ef7fa5beb4e8f1aeb6b8'
  Recommend you wait up to 4 hours, and then run this command again.
failed

Like it says, you'll need to run the command again later. Let's remember to do that:

# at now + 4 hours
at> git annex get my_cool_big_file

Another oddity of Glacier is that git-annex is never entirely sure if a file is still in Glacier. Glacier inventories take hours to retrieve, and even when retrieved do not necessarily represent the current state.

So, git-annex plays it safe, and avoids trusting the inventory:

# git annex copy important_file --to glacier
copy important_file (gpg) (checking glacier...) (to glacier...) ok
# git annex drop important_file
drop important_file (gpg) (checking glacier...)
  Glacier's inventory says it has a copy.
  However, the inventory could be out of date, if it was recently removed.
  (Use --trust-glacier if you're sure it's still in Glacier.)

(unsafe) 
  Could only verify the existence of 0 out of 1 necessary copies

Like it says, you can use --trust-glacier if you're sure Glacier's inventory is correct and up-to-date.

A final potential gotcha with Glacier is that glacier-cli keeps a local mapping of file names to Glacier archives. If this cache is lost, or you want to retrieve files on a different box than the one that put them in glacier, you'll need to use glacier vault sync to rebuild this cache.

See Glacier for details.