How to change the temp location for the OAB Generation process on Exchange 2007 sp2 and Exchange 2010
Dave Goldman blogged how to change the OAB Generation process temp folder. However it only applies for Exchange Server 2007 SP2 and Exchange Server 2010.
By the way, if you are going to change that make sure that you specify the new location in your exclusion list of your AV.
Read more at source: http://blogs.msdn.com/dgoldman/archive/2010/02/06/how-to-change-the-temp-location-for-the-oab-generation-process-on-exchange-2007-sp2-and-exchange-2010.aspx