This error popped up recently while trying to mirror a git repository onto another server. Attempting to clone the repository yielded hundreds of errors like these two:

./objects/pack/._pack-de7d2e641423ddac38ff369dae6afad9f02d4397.idx is too small
error: index file /home/joe/site/.git/objects/pack/._pack-de7d2e641423ddac38ff369dae6afad9f02d4397.idx is too small

Not a lot has been written about this error, and I don’t make any claims to understanding Git’s internals enough to know whether or not that was a very bad thing or just cosmetic. But playing it safe, I assumed the clone had failed and the repository was compromised.

On my machines, I’m running up to date 1.6.x Git binaries, but the server throwing these errors is running 1.5.4.1. I suspected a version imcompatibility, but googling for “git” and any variant of “version” is epic futility. (hint, google “backwards compatible” instead). Here’s what I found:

Sometime around version 1.5.0, Git’s repository format changed. While the notes indicated the server version of Git should have supported this, a Git development patch and the Git 1.6.0 release notes convinced me to try:

By default, packfiles created with this version uses delta-base-offset
encoding introduced in v1.4.4. Pack idx files are using version 2 that
allows larger packs and added robustness thanks to its CRC checking,
introduced in v1.5.2 and v1.4.4.5. If you want to keep your repositories
backwards compatible past these versions, set repack.useDeltaBaseOffset
to false or pack.indexVersion to 1, respectively.

In the local repository’s config, I set repack.usedeltabaseoffset to false and then repacked the repository:

git config repack.usedeltabaseoffset false
git repack -a -d

This appears to have fixed the problem. Cloning the repository worked perfectly and everything seems to be working smoothly now.