Ledmon and ledctl are two utilities for Linux that can be used to control LED status on drive backplanes.  Normally drive backplane LEDs are controlled by a hardware RAID controller (PERC), but when using Software RAID on Linux (mdadm) for PCIE SSD, the ledmon daemon will monitor the status of the drive array and update the status of drive LEDs.

Dell systems use a three-LED status on their backplane.  The activity LED is caused by drive activity, read or write.  Dell uses the following patterns:
 offline  - No LED
 online - Steady green LED
 identify - Slow blinking green LED
 rebuild - Fast blinking green LED
 fail - Orange LED

Ledmon uses the International Blinking Pattern Interpretation (IBPI) specification for displaying which state the drives are in. According to the specification, there can be several states for drive LEDs:
 in critical array
 in failed array

The latest ledmon package ships with RHEL6.3. SLES11 SP2 however uses an older version of ledmon that must be updated in order to support Dell PCIE SSD devices.

Ledmon can be run as a daemon to constantly monitor the status of drives and Software RAID and set the drive LEDs appropriately.  Ledctl can be used to identify an individual drive on a backplane, useful when determining which drive maps to which drive bay slot.  On Dell SSD systems using ledctl and ledmon requires the ipmi drivers to be loaded.

On RedHat Enterprise Linux 6.3:
    # yum install OpenIPMI (or use rpm to install OpenIPMI/OpenIPMI-libs rpms directly)
    # chkconfig --add ipmi
    # service ipmi start
    # ledmon

ledctl usage:
    # ledctl locate=/dev/rssda will blink drive LED
    # ledctl locate={ /dev/rssda /dev/rssdb } will blink both drive LEDs
    # ledctl locate_off=/dev/rssda will turn off the locate LED

If running ledctl and ledmon concurrently, ledmon will eventually override the ledctl settings.

 SGPIO specification: ftp://ftp.seagate.com/sff/SFF-8485.PDF
 IBPI specification: ftp://ftp.seagate.com/sff/SFF-8489.PDF
 Sourceforge project: http://ledmon.sourceforge.net/