Trying to do a physical to virtual conversion so that this blog can be put on the VMWare ESXi 4 box, and the little HP box can do Asterisk (VMWare didn’t play well with Asterisk).
After much frustration (need 32-bit libs on Fedora for the Converter to run), I still couldn’t quite fathom out why the converted machine failed to boot (“cannot find root”), then it dawned on me that the VMWare converter was not finding the root filesystem because it was on a linux raid1 mirror partition, which the converter doesn’t support.

Rather than transferring manually, here’s what I did:
change partition type of RAID partition from type fd (linux raid autodetect) to 83 (linux ext). This might not be necessary, but it should prevent the kernel from auto-configuring RAID for that partition.
cd /etc
mv mdadm.conf mdadm.conf.old (i.e. remove the mdadm.conf configuration file, but keep as a backup just in case).
mkinitrd /boot/initrd-noraid-`uname -r`.img `uname -r`
(basically we’re doing “mkinitrd /boot/initrd-noraid-2.2.15-el5.img 2.2.15-el5″ if 2.2.15-el5 is your running kernel version.. the uname -r substitutes this for us.)
cd /boot/grub
edit grub.conf and change the initrd= line to /boot/initrd-noraid-x.x.x.img, change kernel boot parameter root= to reflect partition without raid, e.g. change from /dev/md0 to /dev/sda2. Do the same for /etc/fstab.

Now the initial ramdisk has no mdadm.conf, and the partition type is no longer set to linux raid autodetect (type fd).
Power down, remove one of the RAID1 disks, and the system should boot and run now off the other disk without RAID.

VMWare converter now works. Job’s a good ‘un.