Asus RS500-E9 Series User Manual page 64

5. Message LED (MESLED1)
This onboard LED lights up to red when there is a BMC event log is generated.
6. Hard disk activity LED (HDDLED1)
This LED is for the storage devices connected to the onboard SATA, or SATA/SAS
add-on card. The read or write activities of any device connected to the onboard SATA,
or SATA/SAS add-on card causes the rear panel LED to light up.
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Chapter 4: Motherboard Information