The first time I tried to do this via the Windows Server Backup GUI, I was surprised that I couldn't backup just the system state on a Domain Controller.

Turns out you need to hit the command line (bit of a reoccurring theme in Windows 2008).

the command to use is :

WBADMIN

Running it from the command line with no options gives us a bit of help:

So how do we backup the system state only?

WBADMIN START SYSTEMSTATEBACKUP -backuptarget:d:

Problem here is that C: is my System Drive and my DIT rests on my D: drive, which means I get the following error message

No extra disks to backup onto, no CDR/DVD drive to backup onto and out of the box WBADMIN will not allow a backup to a UNC path or mapped drive!

However all is not lost!

KB944530 points out that we can backup onto local volumes by tweaking the registry as follows:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wbengine\SystemStateBackup\

Name: AllowSSBToAnyVolume
Data type: DWORD
Value data: 1

Running the same command again works: