I have a git annex repo for all my media that has grown to 57866 files and git operations are getting slow, especially on external spinning hard drives, so I decided to split it into separate repositories.
This is how I did it, with some help from #git-annex. Suppose the old big repo is at ~/oldrepo:
# Create a new repo for photos only
mkdir ~/photos
cd photos
git init
git annex init laptop
# Hardlink all the annexed data from the old repo
cp -rl ~/oldrepo/.git/annex/objects .git/annex/
# Regenerate the git annex metadata
git annex fsck --fast
# Also split the repo on the usb key
cd /media/usbkey
git clone ~/photos
cd photos
git annex init usbkey
cp -rl ../oldrepo/.git/annex/objects .git/annex/
git annex fsck --fast
# Connect the annexes as remotes of each other
git remote add laptop ~/photos
cd ~/photos
git remote add usbkey /media/usbkey
At this point, I went through all repos doing standard cleanup:
# Remove unneeded hard links
git annex unused
git annex dropunused --force 1-12345
# Sync
git annex sync
To make sure nothing is missing, I used git annex find --not --in=here
to see if, for example, the usbkey that should have everything could be missing
some thing.
Update: Antoine Beaupré pointed me to this tip about Repositories with large number of files which I will try next time one of my repositories grows enough to hit a performance issue.