Re: Took the plunge and went SCSI the Cabriolet

[Keith Baker <toaster cybercom net>]

How does linux handle multi-controller environments?  Can you mount the
same partition on two machines?  Are there any advantages?  Whats the
deal?

On Wed, 12 Aug 1998, Quant-X Alpha Linux Support wrote:

> Oachkatzlschwoaf !
> 
> > 
> > I have decided to go with SCSI instead of IDE.  I have not used SCSI
> > before.. I wanted the 2940UW but settled for a Diamond Fireport 40. I
> > also picked up (2) - 1G IBM hard drives without documentation. Any one
> > with knowleged as to where to find info would be appreciated. I am
> > searching IBM now.
> 
> www.storage.ibm.com ?
> 
> > Also, I got some conflicting statements today about SCSI configuration.
> > The manual tells me to set boot drive to ID 0. The guy at the computer
> > store said the higher the number the higher the priority. What is best
> > the best solution? I still have to figure out how these are jumpered
> > too.
> 
> These statements are not conflicting ones.
> IBM is the only company that does "right" SCSI-Setup... 
> So the 1. Harddisk has id 6 in some IBM configurations.
> All other people in the world use ID 0: for the first drive.
> This has lowest priority but this has really no effect at all.
> 
> An (bad ?) example: If you have an old streamer without
>            disconnect/reconnect support it maybe loose
>            the "selection war" if it has a lower SCSI-ID.
>            But if the streamer wins the selection (maybe because
>            no other device wants the bus at moment) nobody can 
>            interrupt it until the next bus free phase (after fully
>            completing a rewind or unload (immed bit not set). command)
>            So a device with a lower id may block higher priority
>            devices, (maybe 30 sec or more) too. But for shure, 
>            if multiple devices want
>            the bus (if the bus is free), the one with the higher id 
>            gets it. It would be theoretically possible that a device
>            never gets the bus because of priority (low id); so to 
>            give at least the host adapter(s) the higest possible 
>            is a good reason.
> 
> I really suggest to use id 0 for the first harddrive and so on.
> It's not worth to care about selection priority in 99.9999% of
> all cases, and most people will do it that way. (This is not
> a real argument !)
> 
> There is another good reason to use "target ID's from 0 up" scheme.
> With this scheme (I used it for all systems I ever build)
> I know that the first disk has always ID 0.
> 
> This doesn't work for IBM's "ID 6" down scheme for a simple reason:
> On multi-initiatior environments (if you want to connect a SCSI disk
> to multiple host adapters (machines) at the same time) the disk
> should have ID 5, because high id's are of interest for host
> adapters.
> 
>   ciao -
>     Stefan
> 
> PS.: I hope that you are totally confused now ;-} 
> 
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