Unity Migration Blog

Weekly defragmentation of the two local partitions for the DC and FS servers has been scheduled for the 4 & 5 AM time frame. WSUS00 runs the process in in 9 PM time frame weekly.

I'll add the script to the other servers in the near future.
-- Joe W.

The Microsoft resource:
http://www.microsoft.com/technet/itsolutions/cits/mo/winsrvmg/adpog/adpog3.mspx
Active Directory Product Operations Guide
Chapter 3 - Detailed Maintenance Actions

provides specifics on the desired number of Global Catalogs in single global domain / single-domain forest environments, quite relevent the Unity AD forest

To the point: "If your deployment uses a single global domain, configure all domain controllers as global catalog servers. In a single-domain forest, configuring all domain controllers as global catalog servers requires no additional resources".

The same resource, in the area with the header "Task: Add the Global Catalog to a Domain Controller", there was mention that all global catalog servers require 0.6 GB of storage.