Have you ever hotplugged a SATA Drive? With new mainboards udev will recognize the new harddisk with no effort, but if you use older hardware maybe you should check your BIOS (switch from IDE to AHCI mode) and type following command in your shell after replacing your SATA drives:

echo "- - -" >> /sys/class/scsi_host/host[2|3|4]/scan

For more information and a safe unmount script look here: http://www.makestuff.eu/wordpress/sata-hotplug-in-ubuntu/