Need help recovering software RAID array

[verbatim]

Well, I had a disk fail in my raid5 mdraid setup, and am having trouble recovering it.
It's a 4 disk setup, with no spares.

I was able at one point to start it with 3 disks and see that the data was fine, but I am now trying to restart it with 4 disks and cannot get it to work.

Running "mdadm --assemble /dev/md0 /dev/sda2 /dev/sdb2 /dev/sdc2 /dev/sdd2" shows "mdadm: failed to RUN_ARRAY /dev/md0: Input/output error", and logs messages to dmesg showing sda2, sdb2, sdc2 as operational in the array, but sdd2 is not. It then says "cannot start dirty degraded array for md0".

Looking at /proc/mdstat shows that sdd2 is in as a spare - which it shouldn't be... it should just be a regular disk.

Running "mdadm -E /dev/sdd2" also shows it as a spare, and the array with a faulty removed disk.

I'm quite worried at this point, but I think I'm still safe... I just can't figure out how to put this thing back together. Does anyone have any ideas? I can provide more details as needed.

Thanks.

[Algernon]

If you are still having this problem...

Start the array in degraded state (meaning missing one) with --fail, so you need to mark one of the drives as failed. This should be the drive that does not contain the data but is going to be added to array.

When up and running add the spare (or new) drive to array.

-M