This script is designed to notify you of disk failures on your FreeNAS server, and light the disk failure LED on your SuperMicro SAS2 backplane. It is unknown whether it will work with other manufacturers' backplanes. It's unlikely this script will work as is in any environment other than a FreeNAS server.
Download the script to someplace on your pool, and make it executable using chmod +x zpscan.sh.
This script should be run as a regular cron job--the frequency is up to you, but I'd suggest between 15 minutes and an hour. The command to run is /path/to/zpool.sh <poolname> [email_address]. The email address is optional; if set, the script will email you on disk failure.
The script runs regularly. If the pool is healthy, it writes a text file to /root/.sas2ircu/drives-<poolname> listing your drives and their locations on your backplane. If not, it writes a text file to /root/.sas2ircu/locs-<poolname> with the locations of any failed disks, turns on the warning LEDs for those locations, and (optionally) sends an email to the specified email address.
Further discussion can be directed to this thread on the FreeNAS forums.