A quick and dirty way to make a specific hard drive LED blink so that it can be identified.
while true; do smartctl -a /dev/<device>; done
The simple trick is to run smartctl in a while loop. The command will run forever until you Ctrl + C. It make the LED blink rather obviously, which made things much easier.
Other method :
To start: ledctl locate=/dev/sdd
To stop: ledctl off={/dev/sdd}
This lives in the ledmon package.