Hi We are using Exchange 2003 and 2007 - same domain, but the E2003 servers are in one site and the E2007 servers in another AD site. We need to reboot a DC in each of the sites. Will this affect E2003/E2007 in anyway? Or will Exchange just failover to another DC? Secondly, does Exchange use DC's or GC's as part of DSAccess? Finally, is there anyway to find out which DC/GC an Exchange server is actually using? Many thanks in advance.

Exchange will only use global catalog domain controllers. If the DC that it is using goes away, then it will look for another DC, but not immediately. Microsoft claim 15 minutes after it has gone away, but I find it is closer to double that. Therefore you can either take the hit, or lock Exchange to a specific domain controller at least an hour before the reboot, and then change it back to auto detect later. Exchange 2003 DC selection http://www.msexchange.org/tutorials/Exchange-System-Manager-Domain-Controller-Selection.html Exchange 2007: http://msexchangeguru.com/2010/05/09/hardcoding-domaincontroller-exchange2007/ Although both of those were found in less than 30 seconds in Google. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources

Thanks Simon. Regarding this statement: " If the DC that it is using goes away, then it will look for another DC, but not immediately. Microsoft claim 15 minutes after it has gone away, but I find it is closer to double that" What is the effect on Exchange during this 15 (or whatever) period? Exchange can use more than one GC can't it?

During the 15 minute period Exchange is effectively dead in the water. Anything that requires a fresh lookup on permissions etc will not work, clients will freeze etc. Exchange cannot use multiple domain controllers at the same time - it locks on to a specific DC and that is it. It doesn't change unless that DC isn't available next time the services start. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources