Backplane LEDs
Backplanes are typically outfitted with Light Emitting Diodes LED to indicate particular conditions. Usually 2 or 3 LEDs are used per drive (or slot).
Activity LED. This LED, usually Green, is used to indicate activity to the drive. Activity means that data is either read or written to the drive. Some equipment vendors will blink the LED at a steady rate during activity (i.e. at 4Hz), whereas others will actually turn the LED on and off synchronously with the actual activity.
Fail/Rebuild/Predicted Failure LED This LED, if it exists, is most often Red. It is turned ON where a failure of the drive is detected. Some vendors also use blinking variations of this LED to indicate a rebuild condition, or a predicted failure condition.
Locate LED This LED, when present, is typically Blue. It is turned on when a user selects a particular drive or drive slot through the storage management software. The locate LED is useful in locating a particular drive or drive-slot where there are large numbers of drives or banks of drives in large computer systems. Some vendors will blink the Locate LED rather than just illuminating it.
Because not all vendors equip every drive slot with 3 LED, combinations of LEDs and blinking patterns may be used to indicate various conditions. If 2 LEDs only exist per drive, the first is typically Activity LED and the second is Fail.
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