in-situ conversion to FT disk config?

[Drew Van Zandt]

I've done this... you use:
mdadm -f -l 1 -C /dev/md0 /dev/hdc1
creating a degraded RAID1 array (partition hdc first).
Now mount /dev/md0 wherever, and copy your data over.  Check to see
it's there and happy.  Then:
mdadm -A /dev/md0 /dev/hda1
(assuming hda partitioned etc.).  It'll rebuild in the background. 
You'll need to tag the partitions as type fd WHILE THEY ARE NOT
MOUNTED to get them autodetected by the kernel; you'll have to compile
RAID into the kernel hard (not as a module) to be able to have your
root fs on the RAID.

--Drew Van Zandt