Asus Pro WS 621-64L SAGE Series Manual page 31

3. Storage Device Activity LED
The Storage Device Activity LED lights up or blinks when data is read from or written
to the storage device or storage device add-on card.
4. BMC LED (Pro WS C621-64L SAGE/10G only)
The BMC LED blinks to indicate that the on-board BMC is functional.
ASUS Pro WS C621-64L SAGE Series
1-17