This tip assumes the ENTIRE disk will be used
First initialize the MBR, and overwrite using the default template:
Note: Substitue sd1 for your disk
Next use disklabel to modify the current partition layout:
Note: p m will display the current partitions on the disk
Delete all partitions except c:
> d b
> d d
Note: The “d” deletes the specified partition. “d a” deleted partiton “a”
Create the new OpenBSD partition on the disk:
offset:  <enter>
size:  34700m
FS type: [4.2BSD] <enter>
Note: Change the 34700m to the full size of the disk you have. The disk in
this example was 34.7Gb in size.
Now build a new file system on the disk using the following command:
Finally, make a directory where you would like to mount the disk.
Mount the disk.