Source Control Management (SCM) is better known as Revision Control Management. Revision control systems currently supported by Redmine include Subversion (SVN), Git, Mercurial, Bazaar, Darcs and CVS.

As mentioned, Redmine integrates SCMs nicely using them not just as source code readers but making more use of them. In Redmine, we can do the following: Associate a revision with issues (having revisions listed on issue pages). Automatically close an issue and/or change its done ratio when an appropriate commit has been made. Use Wiki syntax in commit messages. Refer a revision, a commit, or a file from a Wiki syntax powered content, which can be a Wiki page, an issue description, a project description, or a forum message and much more

But all this makes Redmine a source code browser not a SCM manager (that can be done with plugins however). So why is choosing the right SCM so important?

Unless you are fine with having SCM and Redmine integrated visually most likely you will want a deeper integration when you know the options. Three levels of Redmine and SCM integration can be distinguished as follows:

The basic browser level requires SCM clients to be installed on the same server Redmine is running on so you may want to use only some of the supported SCMs. Also the basic support of SCMs is not equal: revision graph (similar to one on Github) is supported only for Git and Mercurial, however, these two SCMs can be only local (repositories should be on the same server, where the Redmine is).

Redmine comes with Redmine.pm—a Perl module for Apache web server—which can be used to authenticate Subversion and Git users against Redmine. If the Redmine.pm tool has been integrated, you can control who has access to project Subversion/Git repository and what kind of access (read and/or write) they have by simply managing project members (and roles). Something similar (with additional changes made to Redmine and/or system) can be done for Mercurial and Bazaar. Nevertheless Subversion and Git SCMs are best supported by Redmine.pm and their support is out of the box. Most likely you will have problems configuring other SCMs to authenticate against Redmine.

The only missing functionality for Redmine to become a full-featured SCM manager is the ability to create repositories. And such functionality also comes with Redmine and is provided by the reposman.rb command-line tool. This tool supports Subversion, Darcs, Mercurial, Bazaar, and Git (all except CVS). The problem is that in order for it to work you need to create a cron job executing it periodically. Luckily alternative solutions exist and are provided by third-party plugins such as SCM Creator, Redmine Git Hosting, and Redmine Gitosis.

When choosing SCM, you should also consider your requirements, your experience, preferences of your team or audience, easiness or complexity of use and so on. However, the best integratable SCMs seem to be Subversion and Git.