Comment 35 for bug 990913

That's correct, one of the 3 devices is another array. But this setup worked in previous Ubuntu releases. If I remember correctly I created the array in Ubuntu 10.04, and it has since worked in 11.04 and 11.10. It's always been the same array, I know that at least once it was a "clean" new install (new root partition), and from 11.10 to 12.04 was an upgrade in the same root partition.

So something must have changed in the startup scripts that start the arrays for the root device; or in md. And the fact that I can still get it working by re-assembling the array in rescue shell, make me believe it's in the scripts.