Date   : Tue, 29 May 2012 21:52:10 +0100
From   : simon_marchese@... (Simon Marchese)
Subject: Setting jumpers SCSI IDs

On 29/05/2012 20:43, Michael Firth wrote:
>
> On 29 May 2012,@17:21, Jules Richardson<jules.richardson99@...>
 wrote:
>
>> On 05/25/2012 02:40 PM, Pete Turnbull wrote:
>>> On 25/05/2012 10:44, Phill Harvey-Smith wrote:
>>>> On 25/05/2012 10:06, Jim Hearne wrote:
>>>>>> putting a jumper on makes it a value of '1',
>>>>>> and getting it off makes it '0'
>>> Pretty standard for SCSI, especially drives.
>>>
>>>> Yes generally SCSI controller/ host adapter has id 7 and drives have ids
>>>> 0..6.
>>>>
>>>> However if you have an SGI unix box, they decided to have the controller
>>>> as id 0 and drives as 1..7 which can be confusing if you are used to
>>>> what everyone else uses.....
>>> Actually it would be more accurate to say that most non-PC computer
>>> manufacturers use 0 for the controller and 1-7 for the peripherals,
>>> which can be confusing if you're only used to PCs :-)
>> I think Apple also used #6 for the HBA at one point in time. I'm not sure
>> if they actually supported 8 devices on the bus (inclusive of HBA at #6) or
>> if no device could be placed at ID #7.
>>
> I'm pretty sure Apple also used 7 - certainly they had the primary HD as
ID 0. I think they reserved 6 for a CD drive, but I may just be thinking
of Workstation vendors.
>
> Certainly Sun went for this approach - 0 for the first HD, 1 for the second
HD, 6 for the CDROM and 7 for the controller. I think HP workstations had
a similar default setup.
>
> One disadvantage of systems having the controller at 7 is that it ended
up stuck in the middle of the range when things advanced to include wide
SCSI, which has 4-bit IDs instead of 3.

It got even better when you used a SCSI bus as the shared disk in a 
cluster of servers when the default on each server is for the controller 
to be id=7 (for example when running diagnostics) because having 
non-unique SCSI ids on the same bus is a no-no. Therefore in such a 
shared SCSI bus setup the best practice was to set the first controller 
to id 6, the second to id 5 and so on. Of course this was usually done 
with controllers whose id could be set to other than 7 in some way.