The configuration is a revision-managed clear-text file; every change in configuration is made into a new revision; logged with time, administrator, and a message. Configuration changes are always performed via the backend's SOAP API, since it's the only way to interface with the system. This is transparent to the users, who typically uses the web administration or console.
Most of the configuration is shared between all systems with clustering enabled. Shared and non-shared keys are visible on the web administration's Cluster > Configuration overrides page.
The current configuration can be viewed on the Configuration > Plain-text editor page. It can be "backed up" by simply copy-pasting its content. An import can be performed by removing all text that's in the area, and then pasting any desired configuration into it, and pressing Save. It will be applied immediately, without having to reboot.
The configuration revisions are shown on the web administration's Configuration > Revision management page. You can view or download any configuration revision on the revision management page, by clicking on it (or its right radio button).
From the console, you may view and revert configuration. Navigate to the "Configuration Management" section. "R" will revert and "enter" will show the configuration.
The system holds around 1000 changes (revisions) until you need to truncate the revision log. This limit will cause the unit not to be able to do any more changes. A warning message will appear telling you to truncate the configuration.
Go to System > Commands and run the trunksvn command with the oldest revision number you want to save in the input field.