convert legacy array in place?

Hi,

It seems like this should be a FAQ but careful google and mailing list archive searches didn't seem to turn up anything.

I have two machines with legacy RAID-0 arrays created with raidtools.  I have updated one to Fedora Core 4 and now use mdadm.  Am I correct in thinking I have to use "mdadm --build" every boot to access the array?  My mdadm.conf contains

DEVICES /dev/hda1 /dev/hdb1 /dev/hdc1
ARRAY /dev/md0 level=raid0 num-devices=3 devices=/dev/hda1,/dev/hdb1,/dev/hdc1

but the array doesn't seem to come up by itself on boot.

On the same lines, can this array be converted to a new style array just by writing new superblocks, or do I have to do the backup-reformat-restore thing?

TIA.