I have two problems that I believe are related. One has been happening for years through multiple versions of Ubuntu (at least from 11.10 to 12.04), the other is new since I update the kernel.
First problem first, this is the one that's been happening for years. During a normal boot the system will appear to hang on the "purple" screen, but really it's just at an initramfs prompt behind the purple screen. I usually type "exit" and the boot continues as planned, loading into Ubuntu within a second or two. I've always had the suspicion that this hang was due to my novice setup of a RAID array a couple years ago. Something went wrong, I deleted the array and started over and the second time everything was fine. But, that's about the time that this problem started happening. I've lived with it because I only reboot my computer a couple times a year. I can live with typing "exit" a couple times a year...
Second problem, I updated to the latest Kernel (something I hate doing because it ALWAYS gives me trouble, but the tinkerer in me insists that I get the latest updates...) and now after the first error I type exit and then the system hangs showing numerous warnings none of which I feel have anything to do with the actual problem because none of them are about mounting /dev/md/1 (even though it started as /dev/md1 when I created it the array is now known as /dev/md/1). If I change my /etc/fstab to comment out the line about mounting /dev/md/1 everything will start up OK.
Once Ubuntu loads up I have to stop /dev/md1 (that is not a typo) and then
mdadm --assemble --scan will properly start /dev/md/1. I then edit my /etc/fstab so that /dev/md/1 is a device to mount and then run
Nowhere can I find why /dev/md1 is starting but /dev/md/1 is not.
I don't know how to find the logs for previous boots or else I would put the warnings that I'm seeing during boot...
In order to boot into Ubuntu OK I go to a recovery shell remount the filesystem as read/write, edit /etc/fstab to remove the /dev/md/1 mount and then continue with the boot.