After initially booting from disk 1 and following the prompts to format the disk, you’ll reach a prompt where it asks you to remove the install media and reboot. Note that it also says to only remove the media after the machine has reset before you eject- this is important otherwise the disk will not be bootable:
The sequence that appears to work is:
- press Enter
- wait for VM to reset
- remove mounted iso in VirtualBox just as the VM is restarting and you see the VirtualBox logo/BIOS screen
At this point you’re asked what partition to boot from (select 1) and the installer will continue as normal from that point:
If you remove the iso from the VM before it resets, you’ll see the screen to select either the boot disk or the cdrom (the initial installer screen, not the partition selection screen above), and if you select the disk at this point it will not boot (after pressing Enter it appears there’s a few seconds delay where there is a disk sync step, and this needs to complete before the machine resets and when it’s safe to remove the iso).