RE: 3 questions...

quoted

tell kernel which devices to use for your root filesystem (if your 
root is on raid device), by using something like
  append="md=2,/dev/hda1,/dev/hdb1"

I have some partitions with the fd type in raid arrays but 
would like to switch to the manual method you just described. 
These partitions hold data I care about. Is it safe to change 
the partition type:
   - while the array is not active?
   - while the array is active?

I would recommend to umount the array and stop it if you can.  The fd or default 83 (IIRC), is just a label on the disk, and won't destroy data.  I've more experience with labels on Solaris, and have done those "on-the-fly" with no affects though.

Remember (with RedHat Advanced Server anyway), you'd have to actually disable autodetection.  I'm still working on how it works because I'm still unclear whether this is a kernel feature, or just a result of init scripts.  An older RedHat reference:
http://www.redhat.com/support/resources/tips/raid/RAID-4.html

Marco

Shaw, Marco wrote:
[]

Remember (with RedHat Advanced Server anyway), you'd have to actually disable autodetection.  I'm still working on how it works because I'm still unclear whether this is a kernel feature, or just a result of init scripts.  An older RedHat reference:
http://www.redhat.com/support/resources/tips/raid/RAID-4.html

Autodetection works in kernel, before kernel tries to
mount root filesystem.  At this time, kernel looks at
all partitions of type "raid autodetect" to see if this
is a part of an array, and brings up all it can find
(In fact, this seems to be not true sisnce at least on
2.2 here, only root mddev is started while another two
also marked as "autodetect").  The rest is done in
initscripts, after root filesystem gets mounted (kernel
has no clue about initscripts at all).

/mjt