Indeed, before I could even begin to consider using my bootcamp installation inside parallels, the boot camp assistant itself, for some reasons or another, kept failing to create a bootable USB flash drive using a windows 8 iso. My having a macbook air, this is the way to go short of using an external superdrive, which I don't have. Several people complained about the exact same error on apple forums with no working solution to be found, something nondescript and stubborn like "Your bootable USB drive could not be created", period. Some people get this error, some people don't, nobody seems to know why. So what I did was to
create a x64 Windows 8 USB installation drive using microsoft's own Windows7-USB-DVD-tool inside a normal parallels VM of windows 8 x64. If you want an x64 installation, use a 64-bit installation of windows 7 or 8 to create the dvd/usb installation drive. Similarly for a x86/32-bit installation. 15-20 minutes later I had said bootable USB installation drive, no problem there. Now the catch is that Windows7-USB-DVD-tool creates a NTFS USB installation drive rather than a fat32 one like bootcamp. Unfortunately, when you boot the USB Windows 8 installation drive using apple's boot manager (holding alt at boot), you will not be booting using the installation drive's own EFI/UEFI bootloader but indeed apple's own manager/old version of UEFI/whatever, I am not sure. What is sure though is that it will lead to the next problem, namely that when you get to select the partition inside windows 8 setup, the setup will refuse to install it on the GPT partition that the Boot Camp assistant created earlier.
Apparently you need to boot using (the correct?recent?working?) EFI/UEFI to install windows 8 on a GPT partition. Windows7-USB-DVD-tool put a working EFI/UEFI bootloader on the USB Windows 8 installation drive allright, so in theory one could use another EFI boot load other than apple's.
I used rEFInd. It's easy to install (as short as sudo ./install.sh) and it puts itself inside /EFI on your OSX partition. Pretty nonintrusive.I then
installed the shell.efi component found on rEFInd's website to be able to access the EFI shell at boot time and proceeded to try and get it to load the EFI bootloader found on the USB Windows 8 installation drive, but remember this guy is NTFS formatted, and rEFInd only comes by default with drivers for reiserFS, ext3 and ext4, fat, HFS+ and some other, but not NTFS, so
you need a NTFS driver for rEFInd, which you can get from inside the 64-bit Clover EFI tools package (Contents/Resources/EFI/CLOVER/drivers64/NTFS.efi). I put NTFS.efi in /EFI/refind/drivers_x64 and reboot again, enter the shell, and typed
- load ntfs.efi (or wherever it is, you might have to change drive first to your OS X partition using fs0: and then "cd \EFI\refind" and "ls" around to get to it)
- map -r
- blkX: (change drive to the USB Windows 8 installation drive, so X is its partition number, mine was 5 or 6, you'll have to search or inspect the map list)
- load \EFI\BOOT\BOOTX64.EFI
and voilà ! the Windows 8 setup started and I could select the partition created by the Boot Camp assistant.
The setup might ask you to reformat it to NTFS, do it, otherwise you can't proceed. Be careful not to reformat your other partitions. Evidently you're careful and you have a fresh Time Machine backup lying somewhere just in case.