Q: How can I identify which /dev is which physical hard drive? Which drive is which?!?
A: This is an especially good thing to know when you are trying to replace a failed drive in a SoftRAID array! As of Version 0.7.4020 the serial number is displayed on the WebGUI page Disks > Management > HDD Management if the drive reports it.

run this one-liner is bash:
for i in $(sysctl -n kern.disks);do printf "%s\t%s\n" $i "$(smartctl -a /dev/$i | grep "Serial Number")";done | sort
This will output a list of all disks' assigned /dev's and serial numbers.