[CentOS] Hot swapping sata drives

I have a two external USB drives only 1 is connected to centos 5.1 at a time. the USB drive is SLOW compared to SATA. The external drive suppots both connections USB and SATA.

I bought a little $5 external SATA connector that goes into the PCI slot area (does not actually take a PCI slot just the backpanel) and just plugs back into one of the available SATA ports on the motherboard.

When I turn off the external drive and put the other drive on the connection and then power on will SATA handle that automatically? Is there a command I need to run to tell it check for new disks?

Is this possible? Will I have to reboot to get the swapped external disk detected.

jerry