Available disks are: none. (Xserve G5)

Hello,

I'm trying to install OpenBSB 7.6 on an Xserve G5 cluster node.

Using an external USB optical drive, I was able to boot into the OpenBSD
installer. Now, I am stuck at:

Available disks are: none.
Which disk is the root disk? ('?' for details)

I have tried with two different Xserve G5 cluster node, and different
SATA HDDs. I have tried both with the onboard SATA-I controller, and a
SATA-II controller in the PCI-X slot.

Philipp