RAID-5 spare drive: Can't make spare persist across reboot

[David Rea <dave@daverea.com>]

   [First-time poster, done plenty of googling and archive searching
before sending this, so if it's already been covered my apologies in
advance...]

Hello All-

I am running a 3-disk RAID-5 using kernel 2.6.24 and mdadm 2.6.3 under
Ubuntu server 8.04LTS. I'm trying to add a spare drive to the array.

/dev/md0 == /dev/sdc, /dev/sdd, /dev/sda

I want to add /dev/sdb1 as a spare partition, so I tried `mdadm
/dev/md0 --add /dev/sdb1` ... this worked great; running `mdadm
--detail /dev/md0` shows 3 active and 1 spare. Cool!

However, after a reboot, I'm back to 3 active and 0 spare drives. I
tried adding the spare to my DEVICES list in /etc/mdadm/mdadm.conf,
and adding a SPARES=1 attribute to the ARRAY line in that file, still
no persistence. I tried running `update-initramfs -u` after changing
mdadm.conf (per an IRC suggestion) but still no persistence.

-- Is it possible to do what I'm trying to do?
-- Do I need to create the array anew using `mdadm --create` and
specifying "--spare-devices=1 /dev/sdb1" during creation?
-- Will creating the array again risk corrupting the data already present?
-- Is there any way to instantiate a superblock on /dev/sdb1 so that
it can be associated with this array's UUID?
-- I have the ARRAY line (in mdadm.conf) specified by UUID; could this
be causing the spare to be excluded, since it (presumably) does not
have a superblock?

Thanks in advance,
Dave