We are currently an Exchange 2003 environment with 15,000 users. We are planning a migration to Exchange 2010. Our current architecture calls for 6 mailbox/CA/Hub transport servers (each server has all 3 roles) with 2 servers in each of 3 locations. All 3 locations belong to a single site with GB connections between them. Each server(VM) will have 8 cores which allows for 4 cores for MB, 3 for CA and 1 for HT. Recently I read that all the CA servers must be at the same Exchange version and service pack level. This brings up the question of how to upgrade when service pack 2 is released. If all CA's must be at the same service pack level would we have to upgrade all our servers simultaneously? Also, is there a benefit to breaking out the CA/HT role? If we did, this would require us to add an additional 3 servers(VM) - one for each location - for a total of 9 servers instead of 6. Thanks.

Well, all CAS (not CA, please, now I'm having flashbacks to certificate issues) servers should indeed be at the same Exchange version and SP level. So you first upgrade server A, then server B, and so on. A little overlap isn't going to kill anyone - and there's no organization out there that's going to take down all their CAS servers at once so they can be simultaneously upgraded. There are benefits and downsides of breaking out the Hub/CAS from the mailbox server, but my recommendation would be to see how things go with the current plan. If you need to add separate VMs for Hub/CAS later, then do that then. But I don't see anything wrong with your current plan. I'm a big fan of simple. Missy

The proper way to patch the multi-role servers would be to update the internet facing location first. If all three locations have internet facing client access arrays then start with one location and work your way on to the next until all are completed. The first server you will patch needs to be pulled from the Hardware Load Balancer and Activation blocked so that mailboxes do not try to *over to the server. Once patched, reboot the server. You will then want to add the patched server to the Hardware Load Balancer, verify you can connect to it and then pull the second server out from behind the Hardware Load Balancer. You will repeat the same steps to update and reboot and put back behind the hardware load balancer. Since the AD site is stretched, you won't have to worry about having all users connect to one client access server in the location. Hope this helps Jason

The article below will help “There are no technical reasons why having the roles combined like this is “better” than having the roles separated. Exchange 2007 didn’t support CAS and HT on clustered servers, and we took a lot of customer feedback to help us decide that we needed to support that in Exchange 2010. That doesn’t mean that it is better, it means that it is another option, and if it is right for your environment, then great! If not, well, having separate CAS/HT servers (or separate CAS and separate HT servers) is fully supported and is still a valid solution model” ---------Refer to <Patching the Multi-Role Server DAG>Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.