* I used the Windows 10 enterprise evaluation is (Build 10240)
I already have an existing ESP but Windows doesn't want to acknowledge it, apparently.
I created the ESP with GNU parted and mkfs:
parted /dev/sdb mklabel gpt mkpart ESP 1MiB 1024MiB set 1 boot on name 1 "EFI system partition" quit mkfs.fat -F 32 /dev/sdb1
This gave me this result.
After that I rebooted into the Windows (10) Installer, selected the "Unallocated Disk Space" to create a 150GB Volume for Windows which also creates the MSR, a Recovery partition - and a 100MB EFI System Partition.
To 'debug' this (maybe missing a flag so Windows does not acknowledge the existing ESP as valid), I planned to just hit 'next' to immediately abort afterwards and reboot into Linux to print out partitions with parted. Even before aborting the install I get:
Windows installation encountered an unexpected error. Verify that the installation sources are accessible, and restart the installation
Error code: 0xC0000005
(this only happens when creating an own ESP beforehand, the sources are completely ok and undamaged)
I just ignored that for now and rebooted into Linux, this is the point where it get's REALLY weird, beyond the point I can more or less explain what's happening:
Note the 4(!) ESPs, ie. 3 additional ESPs created by Windows. Also other additional partitions created.
But all those ESPs aren't different (in terms of flags) than my ESP.
Ofcourse one could just go with Windows creating the ESP by itself, but sadly the partition Windows creates is FAR too small for my purposes (if someone knows at least how to force Windows to make the ESP XMB big, let me know too, please ;-) )
Also I imagine the future scenario when I have a Linux already installed with ESP and Windows just don't want to accept this partition either.
So how do I tell Windows to please just use this existing ESP?