You are the messaging engineer for your company. Your company has a main office and four branch offices. The network consists of a single Active Directory forest that contains one domain. An Active Directory site exists for each office. All Global Catalog servers are located in the main office. You deploy an Exchange Server 2007 Mailbox server cluster in each site.

You need to plan an Exchange Server 2007 organization that provides the highest level of server fault tolerance for message delivery. What should you recommend?

A.
Install two Hub Transport servers in each site. Create an SMTP site link between the main office site and
each branch office site.

B.
Install five Hub Transport servers in the main office site. Create an SMTP site link between the main office
site and each branch office site.

C.
Install two Hub Transport servers in each site. Install Windows Clustering on each server.

D.
Install two Hub Transport servers and two Global Catalog servers in each site.

Explanation:
For Exchange 2003, MS recommends you have one GC processor core per four Exchange server cores. This isnt a 1:4 ratio of servers or even processors, but of processor cores: a dual core processor counts as two when doing this calculation.

With Exchange 2007, its recommended you deploy one 32-bit GC CPU core for each four mailbox server cores. While the other server roles will influence how many GC cores are required, the number of Mailbox servers deployed will control deployment of each of the remaining roles. Therefore, basing the number of GC cores on mailbox server cores suffices.

The 2003 recommendations are based on DCs running 32-bit Server 2003. Something wonderful happens when you upgrade to 64-bit architecture: Efficiency can double!

Instead of 1:4, you can have a 1:8 ratio between GC processor cores and Exchange server cores. This assumes you have enough RAM installed to cache the entire AD database in memory. Check the GC NTDS.dit file, by default in %WINDIR%NTDS, to determine AD size.

On 64-bit Windows, with its massively larger address space, you can cache even sizable AD databases entirely in RAM. This affords you a significant speed boost responding to queries, along with a dramatic reduction in expensive disk I/O.

http://msexchangeteam.com/archive/2007/03/28/437313.aspx