cannot set rood device with rdev

hi,

i'm trying to set a root device for my embedded device.
my notebook has a sata-hdd so the hdd is addressed as
/dev/sda....
when i try to set the device /dev/hda1 as root device
i get the error:
/dev/hda1: file or directory not found
but i don't want to set the root device for my notebook.
how can i set it for a device on my embedded-machine?

thanks,

toby