bundle exec rake RAILS_ENV=production gitlab:backup:create
The backup will should be created and located here.
/home/git/gitlab/tmp/backups
something like
3407151110_gitlab_backup.tar
Download this file and restore it to the another sever to ensure you have a good backup. A backup that hasn’t been tested is not a backup at all.
To restore a backup
bundle exec rake gitlab:backup:restore RAILS_ENV=production
References:
https://wiki.archlinux.org/index.php/gitlab
https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/raketasks/backup_restore.md