after creating (debian etch) xen child which fstab looks like:

/dev/hda1 / ext3 errors=remount-ro 0 0 1
/dev/hda2 none swap sw 0 0
/dev/hda3 /data ext3 defaults 0 2

root and swap partitions mounted but /dev/hda3 (/data) wasn't so:
1. forgot to create /data dir (dumbass)
still didn't work

ls /dev and no hda3 (and the others) exist! so:
2. MAKEDEV hda

'refresh' fstab
3. mount -a