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Date:      Wed, 25 Feb 1998 19:35:56 +0100 (MET)
From:      Wilko Bulte <wilko@yedi.iaf.nl>
To:        scsi@FreeBSD.ORG
Cc:        tom@sdf.com, blkirk@float.eli.net, hackers@FreeBSD.ORG, scsi@FreeBSD.ORG
Subject:   Re: SCSI Bus redundancy...
Message-ID:  <199802251835.TAA01401@yedi.iaf.nl>
In-Reply-To: <199802251354.FAA18637@silvia.HIP.Berkeley.EDU> from Satoshi Asami at "Feb 25, 98 05:54:20 am"

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As Satoshi Asami wrote...
> (Redirected to -scsi)
> 
>  *   SCSI adapter rarely fail.
> 
> I've seen one that fried itself.  Adaptec 3940UW (the fried chip was
> actually the PCI-PCI bridge).
> 
>  *   It is possible to have up to two host adapters per channel.
> 
> Yes.  We've tried it before, with a couple of patches from Justin
> (since merged to the main source), we could get it to work.  (The same 
> single-ended controllers as above.)

And cross your fingers that the device vendor has correctly implemented
multiple initiator support. Although the SCSI standard says they should this
is in no way guaranteed to work. Crappy firmware is plentiful.

>  *   Someone the freebsd-scsi list is working on this.  Rather than a simple
>  * backup design, he is working on simultanous use of both host adapters at
>  * the same time, by two separate computers.  The two systems communicate to
>  * make sure they don't step on each others toes when accessing the disks.
>  * The idea is to make a fully fault-tolerant cluster.
> 
> We're working on something similar, although not as extensible as what 
> you described.  The plan is to have all disks mounted read-only from
> both systems during normal operation.  When there is a write, it first 
> gets unmounted from one machine before it gets written on the other.

Who will write the CFS ? ;-) (cluster file system)

Wilko
_     ______________________________________________________________________
 |   / o / /  _  Bulte email: wilko @ yedi.iaf.nl http://www.tcja.nl/~wilko
 |/|/ / / /( (_) Arnhem, The Netherlands - Do, or do not. There is no 'try'
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