I am putting together a new machine that will have four Maxtor ATLAS 10K
III KU018L2 hard drives on it. The mother board has two Ultra/320 SCSI
controllers and I will be putting two drives on each controller. When I
power on the system, I would like the system to power on these drives
one at a time to put less of a surge into the power supply.

There are two (jumper) options for these drives:

SS - Stagger Spin
Pins 21-22 - For most configurations this option is not utilized.
Most current SCSI host adapters offer a Start Unit command
enable or disable, which supersedes the functionality of the
SS jumper setting. When the Delay Spin (DS) jumper is
enabled on the drive, the Start Unit command from the SCSI
host adapter will send Start Unit commands to all devices on
the bus at pre-determined intervals. This can help prevent
power supply overload when running several devices on the
SCSI bus.

DS - Delay Spin
Disable Delay Spin: No jumper across pins 11-12 (factory
default). Disabling Delay Spin allows the drive to spin up
when the system is powered up.
Enable Delay Spin: Jumper across pins 11-12. This setting
will prevent the drive from spinning up until it receives a Start
Unit command from a SCSI host adapter. Most SCSI host
adapters have the Start Unit command enabled by default in
the host adapter BIOS. Enabling Delay Spin is only necessary
when you are starting multiple devices at power on.

The SCSI controllers built into the mother board use an Adaptec AIC-7902
chip to implement them.

So I have a some questions relating to the best way to do this.
I expect that the drives will have SCSI IDs 0, 1, 2, 3 (even though I
know I could number them 0, 1 for one controller and 0, 1 for the other).

1.) Should I use the SS mode and hope that means that they would be
started in the order of the SCSI IDs?

or

2.) Should I use DS mode and, if so, does the controller know to stagger
the startup of the drives? If this is the case, would not two drives,
one on each controller, start at the same time? If so, maybe that is OK.

or

2a.) Or must I issue commands to the SCSI controllers to start the
drives? Do I do this explicitly, or do the device drivers do this
automatically? Or is there something in the /etc/rc.d/somewhere (Red Hat
Linux) that does this? How would one induce, from the command line, a
START command to the drive from the command line?

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