On Thursday 28 December 2006 12:06, "Peter Humphrey" <prh@gotadsl.co.uk> 
wrote about '[gentoo-amd64] SATA mdraid woes':
> Then I'm invited to specify another device, or enter a shell. I use the
> shell to say "ls -l /dev/md2", which shows the block device I expect to
> see, but "cat /dev/md2" returns an empty result. If I do that from the
> installation CD I get a dump of the contents of the md disk, so it seems
> that the node exists but it isn't connected to the array /dev/md2.

I have the same symptoms on my RAID 0, although I have a slightly different 
setup.  I am able to boot because although the RAID 0 is a pv in my single 
vg LVM setup, all the data for my root lv is on other disks, but I haven't 
been able to boot unattended for many months now.

Anyway, I have two suggestions for you.  First, use your favorite fdisk 
tool to confirm all your RAID partitions are set to be RAID autodetect; 
some initrds and particularly the kernel code for RAID detection is very 
picky about this.  [Unfortunately, this is not possible for me, since I 
put whole disks into the RAID array; not partitions.]

If that fails to fix the problem, you might create your own 
initrd/initramfs that includes the full mdadm tool and your mdadm.conf, 
because genkernel (and indeed all "mkinitrd"s I've run under Gentoo) just 
doesn't seem to be able to handle all RAID correctly -- in particular my 
setup has never worked, independent of the options I provide the script.

-- 
"If there's one thing we've established over the years,
it's that the vast majority of our users don't have the slightest
clue what's best for them in terms of package stability."
-- Gentoo Developer Ciaran McCreesh