My apologies if this one has been asked before, but googling all the keywords and searching the forums didn't get me too much insight. I'm running Debian and mdadm to control my software RAID.

I have 3 hards drives, hda, hdb, and hdc. Between all of them, I have set up 5 cumulative RAID arrays, with the topic of my question being md1, or what will be my root partition (I hope). I'm trying to form a RAID 1 array of hda1 (my original root) and hdb5 (the mirror of my root). I've formed the arrays with no issues, with md1 being my exception, as it remains degraded due to the error mdadm yields when I try "mdadm --add /dev/md1 /dev/hda1", informing me that hda1 is in use or busy. Fair enough I say, as it is mounted as the current root partition.

So, I follow the walkthrough I have from square one, and edit my grub so that the "root" line is (hd0,0), and the "root=" in the kernel line is "/dev/md1". (My apologies about not having exact read-outs, I'm at work). Grub takes this without issue, and boots.

My problem starts at mdadm trying to create the arrays, where it informs me that it "failed to assemble all arrays", and then hangs at "waiting for root filesystem".

My best guess as to my issue is that mdadm is having some problem mounting my new arrays at boot, as the only one I see messages about is md0, my RAID 0 I've had since I installed Debian. Thing is, when I boot normally (using hda1 instead of md1), all the md0-5 DO mount on their own, and work properly, as I already have them set to be used in fstab (with md1 being the exception- its still degraded).

I was hoping someone could offer me some advice? Thanks in advance.

other than basic testing to get a slim idea on how mdadm works, I don't generally use it. However, I know to have the /boot partition on a software raid, you need to rebuild the initrd to include the raid kernel modules. Perhaps this is also needed for the / partition where you are having issues?
I generally found this step by step to be helpful: http://kbase.redhat.com/faq/FAQ_43_8999.shtm

And this link is Debian specific: http://www.linux-sxs.org/hardware/raid_for_idiots.html

Thanks for the reply!

I ended up blowing it off and simply reinstalling Debian from scratch. The odd thing is, if I setup the system right off the bat on a RAID 1, then it works perfectly fine, and it seems to me to be using all the settings I had before. I have no clue.

I think it was booting the kernel before, though. It just seemed to get stuck when going for the root partition, because mdadm kept failing (for whatever reason) to assemble the raid arrays, even though they would come together perfectly fine if I booted of the normal hda1.