Last month I did a ConfigMgr upgrade from SP1 to R2, with Cumulative Update 4 afterwards. At first sight everything seems to be okay. After a few weeks however, customer was mentioning OSD was very slow at Driver package and ConfigMgr client stage installation. Default deployment before the R2 upgrade was around 45 minutes, but after R2 upgrade around 135 minutes! Lucky me I found the following post on Microsoft TechNet HERE and HERE.
It appears that MS support was able to find a solution for my environment.
Immediately after enabling the "allow clients to connect anonymously" setting on each distribution point the time it took for the MDT Toolkit package to download went from 30 minutes to around 20 seconds.
The support tech was unable to explain why this setting was required following the R2 upgrade in our environment. He verified that in his lab environment he did NOT have this setting configured on the DP and he saw no issue downloading the MDT toolkit package.
As much as I would like to have a root cause for this issue I'm just happy that my OSD process isnt taking 3 hours now!
At customer mentioned this was the solution also. Immediately after enabling the "Allow clients to connect anonymously" setting on each distribution point configured, deployment was done in 45 minutes again. Strange enough I did a lot of R2 installations, and a lot of SP1 to R2 upgrades also, but never had this issue before. Still happy with this easy to implement solution. Thanks again!