Is it possible to set up the standard backup system in SBS 2011 (or Server 2008 R2) to use an internal drive as a destination as well as external drives?
Before you say yes, from my tests and from what I've read on the web, backups with internal drives included as a destination always seems to prefer the internal drive over connected external ones. (Regardless of what drive might be marked as 'active'). So no data ever gets written to a plugged in external drive.
In my opinion external drives should always have priority over internal drives or including them is pointless.
Create a new share on the SBS server you want to backup.
Assign the correct permissions.
Configure Windows Server Backup to point to the UNC path of the share on the server you have created, thus pointing it at itselfs using a UNC path.
So on the C:\ of SBS create a new directory 'SBS Backups', share it, assign NTFS permissions and then point Windows Server Backup to \SERVERNAME\SBS Backups.
Just tried it on SBS 11 it works!