Merge branch 'tmatesoft/gitlab-ce-migrate-from-svn-doc-update' into 'master'

Add SubGit to the tools of SVN migration

Originally from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6549.

See merge request !6803

doc/workflow/importing/migrating_from_svn.md

@@ -4,6 +4,112 @@ Subversion (SVN) is a central version control system (VCS) while
 Git is a distributed version control system. There are some major differences
 between the two, for more information consult your favorite search engine.
 
+## Overview
+
+There are two approaches to SVN to Git migration:
+
+1. [Git/SVN Mirror](#smooth-migration-with-a-gitsvn-mirror-using-subgit) which:
+    - Makes the GitLab repository to mirror the SVN project.
+    - Git and SVN repositories are kept in sync; you can use either one.
+    - Smoothens the migration process and allows to manage migration risks.
+
+1. [Cut over migration](#cut-over-migration-with-svn2git) which:
+     - Translates and imports the existing data and history from SVN to Git.
+     - Is a fire and forget approach, good for smaller teams.
+
+## Smooth migration with a Git/SVN mirror using SubGit
+
+[SubGit](https://subgit.com) is a tool for a smooth, stress-free SVN to Git
+migration. It creates a writable Git mirror of a local or remote Subversion
+repository and that way you can use both Subversion and Git as long as you like.
+It requires access to your GitLab server as it talks with the Git repositories
+directly in a filesystem level.
+
+### SubGit prerequisites
+
+1. Install Oracle JRE 1.8 or newer. On Debian-based Linux distributions you can
+   follow [this article](http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html).
+1. Download SubGit from https://subgit.com/download/.
+1. Unpack the downloaded SubGit zip archive to the `/opt` directory. The `subgit`
+   command will be available at `/opt/subgit-VERSION/bin/subgit`.
+
+### SubGit configuration
+
+The first step to mirror you SVN repository in GitLab is to create a new empty
+project which will be used as a mirror. For Omnibus installations the path to
+the repository will be located at
+`/var/opt/gitlab/git-data/repositories/USER/REPO.git` by default. For
+installations from source, the default repository directory will be
+`/home/git/repositories/USER/REPO.git`. For convenience, assign this path to a
+variable:
+
+```
+GIT_REPO_PATH=/var/opt/gitlab/git-data/repositories/USER/REPOS.git
+```
+
+SubGit will keep this repository in sync with a remote SVN project. For
+convenience, assign your remote SVN project URL to a variable:
+
+```
+SVN_PROJECT_URL=http://svn.company.com/repos/project
+```
+
+Next you need to run SubGit to set up a Git/SVN mirror. Make sure the following
+`subgit` command is ran on behalf of the same user that keeps ownership of
+GitLab Git repositories (by default `git`):
+
+```
+subgit configure --layout auto $SVN_PROJECT_URL $GIT_REPO_PATH
+```
+
+Adjust authors and branches mappings, if necessary. Open with your favorite
+text editor:
+
+```
+edit $GIT_REPO_PATH/subgit/authors.txt
+edit $GIT_REPO_PATH/subgit/config
+```
+
+For more information regarding the SubGit configuration options, refer to
+[SubGit's documentation](https://subgit.com/documentation.html) website.
+
+### Initial translation
+
+Now that SubGit has configured the Git/SVN repos, run `subgit` to perform the
+initial translation of existing SVN revisions into the Git repository:
+
+```
+subgit install $GIT_REPOS_PATH
+```
+
+After the initial translation is completed, the Git repository and the SVN
+project will be kept in sync by `subgit` - new Git commits will be translated to
+SVN revisions and new SVN revisions will be translated to Git commits. Mirror
+works transparently and does not require any special commands.
+
+If you would prefer to perform one-time cut over migration with `subgit`, use
+the `import` command instead of `install`:
+
+```
+subgit import $GIT_REPO_PATH
+```
+
+### SubGit licensing
+
+Running SubGit in a mirror mode requires a
+[registration](https://subgit.com/pricing.html). Registration is free for open
+source, academic and startup projects.
+
+We're currently working on deeper GitLab/SubGit integration. You may track our
+progress at [this issue](https://gitlab.com/gitlab-org/gitlab-ee/issues/990).
+
+### SubGit support
+
+For any questions related to SVN to GitLab migration with SubGit, you can
+contact the SubGit team directly at [support@subgit.com](mailto:support@subgit.com).
+
+## Cut over migration with svn2git
+
 If you are currently using an SVN repository, you can migrate the repository
 to Git and GitLab. We recommend a hard cut over - run the migration command once
 and then have all developers start using the new GitLab repository immediately.
@@ -75,5 +181,3 @@ git push --tags origin
 ## Contribute to this guide
 We welcome all contributions that would expand this guide with instructions on
 how to migrate from SVN and other version control systems.
-
-