I have an environment that has 3 servers. two servers are Domain Controllers and file servers running under windows 2008r2 enterprise. My 3rd server is an exchange 2010 server with CAS, mailbox, and hub transport running under windows 2008r2 standard. I need to upgrade the os to 2008r2 enterprise so that I can build a DAG down the line. I have read that you cannot do an in-place upgrade with exchange installed. My question is: a) is that true? and b) if it is, instead of uninstalling exchange and then doing a disaster recovery of exchange to reinstall, can I simply disable all the exchange services and then perform the DISM in-place upgrade followed by re-enabling the exchange services? All servers are physical servers. This is not a virtualized environment.