And to SVN! https://lwn.net/Articles/194667/

It's not a bad decision; getting POSIX semantics to play well with modern expectations of a highly-consistent and highly-available distributed system is very difficult. But it's a work-intensive decision, and figuring out how to deploy NFS or Ceph at scale might be less work. Especially if Google's SVN/hg developers can work directly with the Bigtable developers on features, and GitLab's developers can't work directly with the S3 team (but can own their own Ceph or NFS stack).

Their Git hosting was also running on that same backend (I was on the team managing those products). But to a previous posters point That is a lot of work both to implement as well as to maintain. If you can just use a distributed filesystem you might save yourself some trouble.