multi scsi questions

[Karl-Heinz Herrmann]

Hello Justin,

On 07-Jul-99 Justin T. Gibbs wrote:
> Multi-initiator environments are becoming more and more common these
> days.  This has been supported in FreeBSD (and just about any 
> comercial UNIX) for some time now.  I would bet that Linux already
> supports it or could be easily modified to do so.

Yes I know that this is what some HA people want to do -- but from
discussions[1] about one month back I got the impression that there is
work done but it's still far from stable or common usage (Linux).

 The priority, from highest to lowest, is
> as follows: 7->0, 15->8.  When a device with an ID lower than 8
> arbitrates along with a device with an ID greater than 7, the device
> with the high ID knows that it has lost the arbitration and will get
> off the bus. 
But from this seems to follow: If there is a device ID 9 and a narrow
device on ID 1 (ID 2 was a typo anyway) the wide device ID 9 recognises
it will loose arbitration and free the bus for an access to device ID 9.
So it won't work.
Or does the high device recognise 

> The device with the low device ID doesn't need to see the high byte
> for this to work.
-> Even if the narrow device with ID 1 is not confused an won't answer
the call for ID 9.

Please keep in mind that I'm no expert on this, just what I picked up
from reading this list[2]. If you have detailed knowledge (like it
seems) please share it.

Especially since I do have a setup with 2940UW and both narrow and wide
devices -- and the Low ID's start to get crowded :-)
Could I indeed switch both wide harddrives from their ID's 1 and 6 to
ones above 8 and still use the (ID-8) by a narrow device?

There were at least strong recommendations never to try that. Some
people had it working but others said it's just because some UW devices
are consistently faster and actually win the race.


Karl-Heinz

----------
[1] maybe this list (aic7xxx at FreeBSD.org) but more probable on one of
    the linux-scsi or some other aic7xxx mailing list.
[2] or linux-scsi or some other aic7xxx 

----------------------------------------------------------
E-Mail: Karl-Heinz Herrmann <k.-h.herrmann at fz-juelich.de>
Date: 07-Jul-99      Time: 18:56:58
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