[ILUG] SCSI [OT]

[David Murphy]

Quoting <Pine.LNX.4.21.0003220005220.4498-100000 at fogarty.spin.ie>
by Paul Jakma <paul at clubi.ie>:

> On Tue, 21 Mar 2000, David Murphy wrote:
> 
>   > try plugging a disk into an SGI an you'll quickly learn that isn't
>   > true. :)
>   
>   Are we talking about an SGI here? I distinctly recollect it being a
>   PC he was using..
> 
> sorry, 'twas meant to be light-hearted. Should probably have worded
> it as "you'll learn that isn't /always/ true"..
> 
> Obviously he wasn't talking about an SGI. SGI's don't support ISA/PCI
> cards /you know/.[1]

Well, maye I'm hallucinating or something, but sgi's web site seems to
list PCI expansion slots in their O2, Octane, and Onyx2 workstations.

> OS doesn't need to support SCAM. it's just a sort of 'plug and play'
> for scsi ID's. Once the ID is set via SCAM, who cares? indeed you
> can set the ID on a SCSI device via SCAM then move that device to an
> adapter that doesn't support SCAM and the device will keep it's SCAM
> set ID. SCAM is a firmware thing, and the device should keep it's ID
> in nvram.

Thing about SCAM is, it allows ids to shift when you add a device -
consider the case of a wide scsi bus with a 16-bit device at 0, 8 bit
devices at 1,2,3,4,5 and 6, and the controller at 7 (So I guess it's
not your SGI ;), to which you add an 8-bit device. This could sit at
target 0, but not at any other address in the 0-6 range. However, the
16-bit device could quite happily work on target 11. So, SCAM can
configure the 16-bit device to t11, and the new device to t0.

Me, I'd expect the OS driver would need to know that devices are
likely to go wandering around the SCSI target space like that, so it
can find its boot disk if it's suddenly moved from t0 to t11, but I'm
happy to be referred to a nice document explaining why that isn't so.

-- 
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"That's a malicious rumour. I'll run over anyone who repeats it."
Stephen Hawking - [http://www.smh.com.au/news/0001/07/features/features1.html]
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