Sorry for the spam. By running sysctl kern.disks I was able to see what went wrong: I have a image based IDE root disk. FreeBSD allocates device ada0 2 times. Once for the Xen IDE device and once for the disk connected to the Marvell passthrough controller. By switching the root device to a Xen bus type the naming changes to xdb0 for the root device and therefore I can now see all Marvell connected disks.