IBM H SERIES RS/6000 - Manual (Page 126)

4. For SCSI disk drives, press the spin-down button on the hot-swap disk drive;
observe the green flashing LED.
5. Unlock the drive by turning the carrier latch 90 degrees clockwise to the open
position.
SCSI Disk Drives
SSA Disk Drives
Attention: SSA backplanes must be fully populated. Each backplane connector
must have a disk drive or a blank carrier installed at all times. If you remove a
disk drive from a bay and do not replace it with another disk drive, you must
install a blank carrier in that bay.
Locked Position
Power
Ready
Check
5-14 RS/6000 Enterprise Server Model H Series User's Guide