There are two ways to restore the backup. The preferred method is with the .unf file generated by backup settings. Alternatively if you have a copy of the /data directory that will allow recovery too.
If you have the .unf (backup) file you can either restore from an active controller (Settings>Admin>Restore) or from the first page of the setup wizard (Browse near the bottom).
If you have the original /data folder (all subfolders and contents inclusive), you can
- stop the controller
- make sure java and mongod are not running (on Windows mongod is rather persistent, so it's best to perform the following steps in Safe Mode)
- copy the new keystore (found in new /data directory) file to the old backup /data directory, overwriting the old one
- delete the new data directory
- copy the old /data directory to the new UniFi installation
- restart the controller
--Data folder locations
Vista+: C:\Users\username\Ubiquiti UniFi\data
XP: C:\Documents and Settings\username\Ubiquiti UniFi\data
Actual directory: /var/lib/unifi/
Symlinked directory: /usr/lib/unifi/data
If the .unf file is really large it may give you an error saying Failed to Start on import or migration. If you have time you can let this sit for a while, and then try accessing the controller. It may import fine. If it doesn't you may need to revert to the original version of the controller, run the pruning script, make a new backup, then either purge and install then restore, or do an in-place upgrade.
We are reviewing database management to alleviate or eliminate this issue. This article will be updated later to reflect that.