Can't re-assemble successfully after creation, initial sync and reboot

[Stephan Stachurski <ses1984@gmail.com>]

I'm having problems with an array that I just created. It's a raid
level 5 with 4 devices using all of the default settings. I'm using
the version of mdadm that's included in ubuntu 9.10 repositories.

When I reboot the machine, /proc/mdstat shows this:
md_d0 : inactive sdc[2](S)

I can stop the device, and attempt the --assemble the array correctly,
but something still is wrong:

$ sudo mdadm --stop /dev/md_d0
mdadm: stopped /dev/md_d0
$ sudo mdadm --assemble /dev/md0 -fv /dev/sda /dev/sdb /dev/sdc /dev/sdd
mdadm: looking for devices for /dev/md0
mdadm: /dev/sda is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdb is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdc is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdd is identified as a member of /dev/md0, slot 3.
mdadm: added /dev/sdb to /dev/md0 as 1
mdadm: added /dev/sdc to /dev/md0 as 2
mdadm: added /dev/sdd to /dev/md0 as 3
mdadm: added /dev/sda to /dev/md0 as 0
mdadm: /dev/md0 has been started with 3 drives (out of 4).
$ sudo cat /proc/mdstat
md0: active raid5 sda[0] sdc[2] sdb[1]
2930287488 blocks level 5, 128k chunk, algorithm 2 [4/3] [UUU_]

md_d0: inactive sdd[3](S)
976762496 blocks

Why, if it correctly identifies the devices that are members of
/dev/md0, and then adds them to /dev/md0, do I not get the complete
array?
--
Stephan E Stachurski