Comment 1 for bug 247027

The same here. The dmraid devices (in my case /dev/mapper/isw_bgjcdcfheh_volume*) are not there when the boot scripts try to mount rootfs.
Only /mapper/control is there.

"dmraid -ay" at the busybox prompt creates all dmraid devices under /dev/mapper/ (and triggers udev to create my LVM volume devices which sit on top of the dmraid array) and the system boots fine after exiting the busybox.

BTW, this works fine under Debian Testing and SID, so it's probably introduced by Ubuntu specific patches. It also worked fine unter Gutsy.