While working with a client, I recently promoted a new Windows 2008 R2 virtual server to a domain controller. Prior to running dcpromo.exe everything looked and performed great, but I noticed a large amount of system resource issues following the promotion. I also ran into several cases of not being able to open various management console snap-ins or other applications. After troubleshooting various issues I finally decided that they all must have had a singular root cause.
After digging around in the event viewer and scratching my head a bit, I asked another network engineer what I was missing. He looked around for a few minutes and asked me if disk quotas had been enabled via group policy. I opened up the Group Policy Management console on another server and discovered a disk quota group policy object for terminal servers that had been applied to the Domain Controllers OU. After excluding the new domain controller from receiving the policy, and then manually removing the existing disk quota entries the server was running at full speed with full functionality.