Installing on extended partition

[Parodper]

Hi,

I am trying to install the 2021 ISO on a computer with multiple OS 
already installed (IDE 150GB HDD), so I was trying to install Debian on 
a extended partition.

Since Hurd does not have USB support I tried installing it from a Live 
USB with qemu --hda /dev/sda --cdrom debian-hurd.iso. This does not 
work, because when I try to format a partition the format stays «do not 
use the partition», and when I try to go back to the main partman menu 
the drive disappears.

You can reproduce this running the installer and filling the 3 primary 
partitions, and then trying to create a extended partition.

After that I tried booting directly from the USB and loading the ISO 
(which I had dd'd into a partition) from the hard drive. The problem 
with this is that partman  does not recognize the existing partition table.

Testing on a faster computer I think I can solve the first problem 
partitioning first from the Debian/Linux installer. However QEMU is too 
slow (takes quite a few hours to reach partman), so I would like to know 
if someone knows of a faster solution.