Git does use transactions, in a pretty clever way: the main storage is immutable -- so when you do a new commit, it creates all new files, and as a last step, u

Git does use transactions, in a pretty clever way: the main storage is immutable -- so when you do a new commit, it creates all new files, and as a last step, updates HEAD/branch, using "rename" call which is atomic on all filesystems. So you can do pretty bad things to git and it would still work. Atomic snapshots are absolutely no problem. Copying the directory while in progress is fine. If you try very hard, you can still make a bad backup -- say you were copying files from remote host, and backup got interrupted after HEAD but before the new data. In this case, there is reflog -- append-only file which keeps HEAD history. Using this file, you would be able to manually recover into previous state.