Multiple TFS_Configuration databases on a single SQL instance

I have been doing a number of upgrades over the last couple of months and have found that doing a migration to a test/dev environment is a good way to gauge the downtime needed to perform an upgrade on the TFS Collection databases.

This works well if you have a spare set of servers / VM's lying around and you are able to do a full migration. I have been in a situation where a new application tier was not much of a problem, but they had an enterprise SQL server setup that we "had to" use.
Even though the "duplicating" of the collection databases is no problem at all, the tfs_configuration database is a different story.

The options are:

1. Install a temporary SQL server on the application tier and simply use that for the tfs_config database or
2. Duplicate the tfs_config and then either "point" tfs to the instance in question or select the correct database during (re)configuration

To perform option 2,  simply create a backup of the tfs_configuration database and restore under a different name (on the same server). When you perform an upgrade or (re)configure the TFS application tier you have the option to select the "correct" config database:

If TFS is already configured and you want to change the database after the fact you can follow these steps:

1. Open up command prompt (run-as admin)
2. Go to the TFS tools directory (for 2015 the default is C:\Program Files\Microsoft Team Foundation Server 14.0\Tools )
3. Put TFS to "sleep" : TfsServiceControl.exe quiesce
4. Backup and restore the config database to the new name
5. Re-register the database : tfsconfig.exe registerdb /sqlInstance:<<sql-server>> /databaseName:<<new config db name>>
6. Finally, wake TFS up : TfsServiceControl.exe unquiesce

That should have TFS pointing to the new config database, meaning you can have multiple TFS instances using different configuration database hosted on the same SQL server.

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