Well, when I first read your post, I thought you did something completely wrong, since I never use md in such manner. However, after I spend a bit of time reading the man page, I realised, what you did is something I never done before, and since I never done such setup before, I should keep my mouth shut and let other more experience users to give suggestions (I am hoping to read others input so I can learn something new). Surprisingly, none came forward...
Anyway, perhaps a little background on how I usually setup my software raid. What I will be talking here will be just a simple raid1 configuration.
1) Use fdisk or cfdisk to partition the disk into the structure that I like. For example, 4 partitions: sda1 sda2 <sda5 sda6 sda7> (where sda2 is an extended partition and sda5 to sda7 is logical partition. sda1 is primary partition).
2) Do the same for sdb with same partition size. So, now sda1+sdb1 will be md0 and mount as /. sda5+sdb5 is /var/ will be md1. sda6+sdb6 is /home/ will be md2. The last group will be used for swap, md3 (sda7+sdb7).
From here, I run mdadm to create the md devices and make sure my fstab is correctly setup (usually is done by the installer, there should not be much for me to work on it).
For your case, you are creating a partitionable
software array, as I quote man page:
If the option to "auto" is "mdp" or "part" or (on the command line only) "p", then mdadm will create a partitionable array, using the first free one that is not in use, and does not already have an entry in /dev (apart from numeric /dev/md* entries).
If the option to "auto" is "yes" or "md" or (on the command line) nothing, then mdadm will create a traditional, non-partitionable md array.
So, basically, I have been setting up my raid as a traditional method. Yours to me is new, as I never try such setup. I am not even sure about what does partitionable
means. Does this mean, I am suppose to run fdisk to /dev/mdp0 (if I name it such) before I can really use it?
However, computer do not lie, if it said as not found, it means, it really
not found. Have you check the /dev/ directory and verify md devices are there? Could it be, for your setup, all your devices are in /dev/md/ folder?
Anyway, good luck, hope someone else able to provide a better suggestion than me.