I'm going over our architecture for another run at upgrading to Exchange 2010 (looked at it about 18 months ago, but budget was cut), and I had a question about how to input the data for our environment. We've got 3 main global datacenters (US/UK/Brazil). We've got 5000 mailboxes in US, 1500 in Brazil, and 3500 in the UK, and I was trying to think of how to put those into the storage calculator. For company politics reasons, I can't consolidate the mailboxes anywhere, but we do want the US site to be passive for the other 2, and the UK to handle passive for the US. All my users will have the same profile (5GB mailboxes, 50 messages/day IO). My root question is, should I make each region a mailbox tier? Or was there another way to account for the unbalanced sites? Thanks in advance...

Okay, so treat each region as it's own DAG with it's own servers?

More like treat each DAG as if it were separate.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."