I'd like to share my setup for keeping bup repositories in git-annex.¹ I'm not sure if this is a good tip, so comments are welcome.

The purpose of this setup is to (kind of) bring encryption to bup, and make it easy to keep bup backups in untrusted storage by making use of the encryption modes and backends provided by git-annex. This approach can be used to make encrypted backups of bup repositories; it can not replace encrypted filesystems such as EncFS or S3QL which wouldn't necessarily require local bup repositories but also can't be combined with storage like Amazon Glacier.

To add a bup repository to git-annex, initialize a regular indirect git-annex repository, and make the bup repository a subdirectory of it.² Then git annex add $BUP_REPO/objects/packs, i.e. the location of the large data files (.pack & .par2). The rest of the bup repository should be tracked by Git (git add $BUP_REPO).³ This way the repository stays fully functional.

After a bup-save the following steps will synchronize all remotes:⁴

git annex add $BUP_REPO/objects/pack
git add $BUP_REPO
git commit -m "Backup on $(date)"
git annex sync --content

In my current setup, the git-annex repositories are located on a local file server. Various clients use bup to create backups on the server. This server also makes backups of other servers. Afterwards, it uploads the annexed data to Glacier (via an encrypted S3 special remote), and pushes the small Git repositories to an S3QL filesystem and another off-site server. Using these repositories (and my GPG key) the bup repositories could be recovered.

It may be important to note that in order to be able to access a bup repository, all files have to be available locally. Bup will not function if any pack files are missing (maybe this can be improved?).

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¹) Not to be confused with git-annex's bup special remote.

²) You can't initialize git-annex repositories directly inside bup repositories because git-annex will (rightfully) identify them as bare git repositories and set itself up accordingly.

³) I've come up with these .gitignore rules to exclude potentially large files not needed for recovery:

/bup_repo/bupindex*
/bup_repo/objects/pack/bup.bloom
/bup_repo/objects/pack/midx*midx
/bup_repo/objects/tmp*.pack
/bup_repo/index-cache/

⁴) git annex sync might not be the safest command to use because it would merge changes from the remotes. However, assuming normal bup usage, external changes to the bup repository are not to be expected.