Comment 15 for bug 420992

update

Installed Oneiric from CD onto one of my machines with dmraid (theone with the Promise Fasttrak100 chipset). The live CD found all partitions OK and offered to upgrade the existing 10.10 Maverick installation. So far, so good.

At the end of the process grub-installer tried to set up grub on sda. No luck, but it did come up with a screen asking me where I would like to see grub. At that moment I was happy and confident things would go right, since the pull down menu showed all the right entries.
I chose /dev/mapper/pcb_jcchiiab, which is the raid set's mbr as opposed to one of the partitions.
The installer obliged -it seemed- and finished without further messages.

Alas, after rebooting I got a grub shell prompt. It seems the installation did not replace the part of grub living in the MBR, so it does not load the stage that actually boots my OS.
I'll try and get into a root shell and reinstall manually, that did help me out before.

Will report back and let you know.

cheers
Tom