[CentOS] Linux Software RAID 1 - Unequal Sized Hard Disks

Has anyone created or rebuilt a Linux Software RAID having mirrored
partitions on unequal sized hard disks ? There is  a CentOS 5 server
having two 400 GB hard disks with five mirrored partitions (software
RAID 1) and one of the hard disks is dying. Since new 400 GB HDDs are
not available here, we are exploring the possibility of replacing the
faulty hard disk with one of a higher capacity (500 GB or more). And
once it is fully replicated, we plan to replace the other 400 GB HDD
also with another hard disk of the same higher capacity.

Just want to know if anyone has done something similar and what are
the chances of success (or data loss) ?

Thanks,
--
Manish