The new content distribution functionality in Configuration Manager 2012 gives you the ability to span a single site across multiple geographical locations using WAN links more efficiently. A well-designed System Center Configuration Manager hierarchy is more likely to contain fewer, flatter, simpler, and easier ways to manage sites. The top site can be a single primary site or a CAS. A primary site cannot have another primary site as a child site. If you want to extend your Configuration Manager hierarchy with a primary site, you need to create a CAS. The reasons to create additional sites are given as follows:
Exceeding the number of clients that a single primary site can handle
An additional primary site distributes the load and reduces the impact of a primary site failure
Locations that use different language versions of the Configuration Manager client and system software
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