Tuning Microsoft PXE/TFTP for Faster Boot Times

MS did not make a big deal of it, but Server 2008 introduced some impressive improvements in PXE boot and TFTP performance.  This was accomplished by enabling TFTP boot clients to “chunk” files into multiple streams or “windows”.  You also can change the size of the TFTP blocks (larger for performance, smaller to reduce packet loss):

http://technet.microsoft.com/en-us/library/cc731245(WS.10).aspx

Use:

bcdedit /enum all /store </pre>

To enumerate the current boot store parameters.  The path will resemble:

c:\RemoteInstall\boot\x86\default.bcd

But you will need to change this based on the location you chose when you installed WDS.

Use:

bcdedit /store c:\RemoteInstall\boot\x86\default.bcd {68d9e51c-a129-4ee1-9725-2ab00a957daf} ramdisktftpwindowsize 8

To increase the number of TFTP chunks, or windows, to 8 (up from 4). I have found that in our environment, “8″ provides a significant PXE Boot performance increase. Anything beyond 8, though, and clients on lower-speed (or perhaps more congested) networks start to experience significant performance degradation.

Use:

bcdedit /store c:\RemoteInstall\boot\x86\default.bcd /set {68d9e51c-a129-4ee1-9725-2ab00a957daf} ramdisktftpblocksize 512

To reduce the TFTP blocks down to 512 bytes in size… this may not be at all necessary in your environment.

After you have made changes run:

sc control wdsserver 129

to signal WDS to rebuild your boot files.

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