Sharding was introduced into GitLab in version 8.10 with modifications in 8.13. The fundamentals of sharding can be found in the GitLab Documentation under Repository Storage Paths.
The summary of the documentation being as such:
- Storage targets must be defined in the
gitlab.rbconfiguration file within thegit_data_dirsparameter. - Selection of targets for random new project assignment is done through the 'Application Settings' under the 'Admin Area'.
We use chef to configure the storage shards that we have, these configuration
settings are applied via the gitlab-base chef role internal link.
The how-to instructional documentation for re-balancing git project
repositories between gitaly storage shard node file systems is here:
https://gitlab.com/gitlab-com/runbooks/-/blob/master/docs/gitaly/storage-rebalancing.md