problem with mdadm not remembering config

[tom hall]

hi, ive built about 5 RAID systems recently, but have hit trouble with
the latest not remembering the raid config after some number of
reboots.
i have a fairly simple setup, 4 drives, raid5 array on /dev/sd[abcd]5
(on an nvidia controller) and mdrun used to run fine (i had no
mdadm.conf file)
i think the mdadm.conf created is wrong, and the script in
/usr/share/mdadm seems to read it as 3 drives + spare or something.

is the advice at http://deb.riseup.net/storage/software-raid/ still valid ?

if i get get a correct (as far as i can tell) mdadm.conf is there any
reason that it should not survive rebooting as many times as i want
to?

most recently when the raid went down, i had to re-add the 3rd drive
(using webmin) to get it back up. is there a problem with using webmin
for this?, as i like it.

all a bit strange, what happens if i boot now with no mdadm.conf, does
one get created, id like to be able to clone the systems easilly

i noticed in the first digest of this list i recieved "kernel
autostart" is this mdrun or something else?

what setup would people recommend for the simple raid setup ive outlined?

cheers, tom