Context: git annex "rules"

First, I have to tell that git-annex is a big win so far (provided you have required git and other knowledge).

My main use case for git-annex contains around 260,000 annexed files, for a total of 1.3 terabytes.

Tried regular git on a subset of it and extrapolated. Count 6-30 hours for simple operations like git status. Plus huge space used for compressed copies of files. All on current hardware: Intel i7 2.5GHz, 16GB RAM, hard disk raw performance 50-100+ MBytes/s.

Using git-annex is a big win :

  • git status take not hours but about one to a few minutes (mostly thanks to decoupling voluntary data change and accidental data corruption and handling them at different times)
  • No space wasted.
  • "Just ask" push of data to remotes to maintain the required number of copies.
  • Easy fetch of missing data from remotes.
  • Corruption detection turns bad data into missing data which can just be fetched again.
  • Data is still there and readable without git-annex or even git.


One to a few minutes for a git status is still long. It is faster the second time (seconds) but still. Can we reduce time for git status ?

This questions looks not git-annex specific.

"Making git status fast is a git-level question". In a sense it is, though git-annex repos are an extreme case of git-repository as they contain in most cases a lot of symlinks which look like small files at the filesystem level.

Which makes the question more filesystem-level anyway, yet relevant to ask here.

Required features of a filesystem

git-annex basically needs a filesystem that allows:

  • long file and directory names (hash in .git/annex/objects directory and file names)
  • long total paths
  • symlinks
  • hard links
  • unix permissions (to make hashed files immutable)

More details e.g. on day 188 crippled filesystem support

Wished features of a filesystem

Fast operations!

Reiserfs, reiser4, btrs are said to be very efficient whe dealing with small files and symlinks thanks to Block suballocation.

Question, restated.

  • Some users of git-annex will dedicate whole hard drives to git-annex repos, like I do.
  • Reading big files (from megabytes to gigabytes) from any decent filesystem implementation will yield similar performance.
  • Which leaves us to choose the filesystem based on safety and performance of reading a git repository with 100k to 1M symlinks.

Can anyone recommend a filesystem to use for fast git-annex level operations ?


Based on previous experience:

  • ext4: default choice, good. Why chase for better?
  • "challenger filesystem X": might get better performance today (X=btrfs, X=reiser4)... or not. Might get dropped in the future (X=reiser4,X=btrfs). Might have bugs? All this might not be actually important, just do another git clone and reformat your drive to the new filesystem of the day.
  • btrfs: might waste a lot of space and actually have slower performance
  • xfs?
  • a small and lightweight partition for metadata with a high performance filesystem and .git/annex/objects symlink to the big data-dedicated filesystem. Might be better because of smaller head movements back and forth. Size has to be decided in advance.

Or perhaps all this is just nitpicking.

Any thoughts?