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Monday, July 28, 2014

Speed up loading the PXE boot image on SCCM 2012 R2

When loading the WINPE boot image with PXE from your distribution point, you might be able to speed up the boot time by increasing the TFTP block size.

In my test scenario the boot time was one minute faster after the change, and this is often a part of the OSD installation where we are actively waiting, so faster boot time are more than welcome.

On the Distribution point with PXE support find the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\DP

Create a new DWORD value RamDiskTFTPBlockSize and use the values 4096, 8192 or 16384 depending on what gives you the best performance in tests.

Start with the value 16384 decimal.



After changing/adding the value restart Windows Deployment Services Server.


And then test to see if the boot time is faster.


Please note that you might find older hardware that wont work with larger TFTP block sizes, so test carefully.


  1. Great post Lars -

    One comment: Remember not to define values higher than 16384. Values higher than 16384 mostly result in a timeout because it is not supported by the protocol implementation.


  2. Great post...

    I have seen that VMware legacy NIC doesn't work with this high TFTP block size - so if your using VMware often to install/capture a image - you will have to make 2 reg files to fast switch between.

  3. I have seen that VMWare and some tablet Pc's cannot PXE boot if the value is higher that 8192. But it is still much faster than with the default value.