OpenBSD: Destroy a Softraid Partition

Booting an OpenBSD's installation media and trying to remove previously created softraid partitions may end up with the following error:

disklabel: ioctl DIOCWDINFO: Open partition would move or shrink
disklabel: unable to write label

Here is how to resolve this issue...

The problem is that the device nodes (in the /dev directory) are not created automatically by default after the installation media boots.

Here is how to create the device nodes manually:

$ cd /dev
$ sh MAKEDEV sd0
$ sh MAKEDEV sd1

...continue for as many nodes as necessary.

Now, it is possible to detach an sdX softraid0 partition (will destroy data):

$ bioctl -d sdX

And finally, to edit the disklabel of disk sdY (will destroy data):

$ disklabel -E sdY
d a
d b

... and continue for as many partitions as necessary.