If you want something with a gui I think Knoppix
http://www.knopper.net (~700MB) would be in order. That supports just about everything and you can drag and drop.
If a cli is all you want, download grml-small
http://www.grml.org (~50MB) and copy it over that way.
boot grml
mkdir /mnt/disk1
mkdir /mnt/disk2
mkdir /mnt/raid
mount /dev/hda1 /mnt/disk1
mount /dev/hdc1 /mnt/disk2
mount /dev/sda1 /mnt/raid
rsync -aWv /mnt/disk1/* /mnt/raid
rsync -aWv /mnt/disk2/* /mnt/raid
This may not be correct howto. Use judgement.