IBM H SERIES RS/6000 - Manual (Page 122)

e. Move the carrier latch to the locked position. If the carrier does not lock,
check that the drive carrier is fully seated in the backplane. When the drive
carrier is fully seated, the green LED on the drive carrier illuminates.
SCSI Disk Drives
The following table explains the meaning of the green and amber status LEDs
and spin down button on a SCSI disk drive.
Status LEDs
LED or Button Status Definition
Amber On Drive spinning
Off Drive not spinning
Green On Power On
Off Power Off
Blinking Power Off/Drive identify
Spin down Depressed Spin down drive and remove power
5-10 RS/6000 Enterprise Server Model H Series User's Guide