Important Hotfixes when running Exchange 2013 on Server 2008 R2 and Server 2012

Additional pre-reqs needed above and beyond exchange requirements
.NET Framework 4.5.1 deployed on all Exchange servers with CAS role
If .NET Framework 4.5.1 cannot be installed, a hotfix for .NET Framework 4.5 is required

KB2745583 – windows server 2012 Download
KB2745582 – Windows server 2008 r2 Download

Decreases CPU spent in .NET garbage collector
Benefits Mailbox & multi-role
Enable by installing hotfix and setting regkey:
HKLM\Software\microsoft\.NETFramework\DisableRetStructPinning (REG_DWORD) = 1

A hotfix is now available for Windows server 2012

Adds two control codes to determine which node owns the GUM lock and which node(s) is/are stuck

KB2779069