SCSI dynamic power management
Quoted 6 lines · James Smart
Also, don't forget that you need to sequence spin-up. A jbod tower with multiple drives all spinning up concurrently can overload the power supply. Most towers avoid this at power-on by having drive jumpers sequence the drives. This is a hard nut to crack as it requires some notion of physical packaging. When I worked on this in the past, the only reasonable approach was to sequence based on target id.
What happens during an ordinary system resume? Don't the drives all get spun-up concurrently then? Or does the sd_start_stop_device() routine wait until the disk is fully spun-up before returning?
Alan Stern