Default out-of-the-box booting on WinPE with SCCM 2012/2016 is quite slow; I’ve seen boot times up to 20 minutes.
This is because System Center Configuration Manager 2012/2016 uses small TFTP block sizes of 512 bytes.
This behavior is set because it’s compatible with all network configurations; but the result is that the PXE boot speed can be very slow using Operating System Deployment with SCCM.
To increase the PXE boot speed, we need to modify TFTP Block Size.
In the registry editor:
Path : HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\DP
Name : RamDiskTFTPBlockSize
Type : REG_DWORD
Value : 16384 (decimal)
16384 is the maximum supported value.
If it is bigger, you can have corrupted data.
However I recommend to do some test with values :
Depends on your network configuration, a lower value can be used.
Restart the Windows Deployment Services Service. (WDS)