Apple Workgroup Server 9150/120 - Manual (Page 57)

10 Attach the bottom of the drive to the bracket, using the four screw holes in the bracket plate.
IMPORTANT Be sure to install drives in the order which they are lettered, filling
slot B before slot C; slot C before slot D; and so on. Because of heat considerations,
it’s important that you use slot E only after the other four slots are filled.
C
D
E
Connecting hard disks and other SCSI devices 41