Exchange Updates installing slow on Windows Server 2012 R2

For customers who are running on R2, we want to make certain you are aware of a condition which can substantially increase the amount of time it takes to install Exchange on this OS. Working with the .Net team, we have discovered that systems which have applied Windows KB3097966 can take 50% more time to install Exchange. The .Net team is working on a resolution to this and will include a fix in a future product . In the meantime, customers who have deployed this Windows can take a one-time action on their server before installing Exchange or a Cumulative to bring installation time back to normal. This procedure needs to be done once on every Exchange server running Windows Server . The command to execute is:

“%windir%\.NET\Framework64\v4.0.30319\ngen.exe update”

Errors and warnings encountered running this command can be safely ignored provided the final exit status code of 0 is reported in the output.