How boot HPE ProLiant DL160 Gen9 into Win2012R2 Repair mode ?

[MThorell]

An automatic (Windows update) reboot last week seems to have crashed our DNS and DHCP services in our domain controller (HPE ProLiant DL160 Gen9, Windows 2012 R2). It is not possible to login to it (via RDP or directly on the machine) with any domain account (error message claims no login servers are available), shares are not available and printer queues are not available neither.
Nobody has the local Administrator-credentials noted down so I need to start up the server in Windows 2012R2 repair mode to manually reset the local Admin password. I have managed to do that (manually fixing the 2012R2 installation USB drive to boot in UEFI-mode according to chapter 4 in "UEFI Deployment Guide for HPE ProLiant Gen9 Servers" and the USB boot chapter in "UEFI System Utilities User Guide for HPE ProLiant Gen9 Servers and HPE Synergy", pen drive in NTFS format instead of FAT32 since the install.wim file is around 5.73 GB), but it refuses to boot from my USB pen drive in UEFI mode. If I try to boot in Legacy mode, it boots, but I do not have access to the RAID array (even after manually loading the drivers).
So clearly I am missing some step to make the pen drive to boot in UEFI mode but I am not capable of finding out what it might be.

[MThorell · Accepted solution]

Right, I finally figured it out, booting in UEFI-mode from NTFS doesn't or (legacy mode works though).

So the solution for was  to prepare the pen drive properly (in FAT32) and split the big install.wim file using the dism command, like this (executed on a Windows 10 Prof. machine) :
Elevated cmd.exe :

diskpart
list disk
select disk (as identified as the USB drive above)
clean
create partition primary
select partition 1
format fs=fat32 quick
active
exit

And then (assuming all windows installation files copied from .iso to c:\temp\ ) :

dism /split-image /imagefile:c:\temp\sources\install.wim /swmfile:c:\temp\sources\install.swm /filesize:4095 /checkintegrity

Finally copy all files from C:\temp\ except the original install.wim to the pendrive and it works fine in Rerpair mode !

Cheers !

/T