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Date:      Mon, 14 Oct 1996 11:58:59 -0400 (EDT)
From:      Brian Tao <taob@io.org>
To:        Stefan Esser <se@zpr.uni-koeln.de>
Cc:        FREEBSD-SCSI-L <freebsd-scsi@freebsd.org>
Subject:   Re: Wonky controller or drive?
Message-ID:  <Pine.BSF.3.95.961014114553.2494F-100000@rogue.io.org>
In-Reply-To: <199610141501.RAA00816@x14.mi.uni-koeln.de>

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On Mon, 14 Oct 1996, Stefan Esser wrote:
> 
> Hmm, adding the 7th drive caused problems ???

    No, not precisely.  This is the history:  sd1 was a 4GB Quantum
Atlas to begin with.  That one died during a power outage about a
month ago.  I replaced it with a 1GB drive in the meantime.  That's
still seven devices.  I only recently replaced it with a new 4GB
drive, since we were running out of room on the 1GB (Web and FTP
server logs, mostly).

    The cable configuration hasn't changed, just that one drive.  sd0
and sd1 (1GB boot drive, plus the new 4GB drive) are mounted
internally in the PC (50-wire ribbon cable, about 40 cm).  The
remaining drives are in two daisy-chained external enclosures, total
cable length of about 150 cm (two lengths of external cabling, two
lengths of internal ribbon cabling), out to the last drive.  The
internal chain is terminated with jumpers on the Quantum.  The
external chain has an active terminator plugged into the last
enclosure.  Each enclosure has its own power supply and fans.  One has
four bays (three drives) and the other has two bays (two drives).

> I guess this is the largest disk capacity that 
> ever got connected to a single 53c810 ... :)

    SCSI bus speed isn't a consideration for our FTP server... I just
needed the mass storage.  :)

> I expect this to be caused by either a too
> long cable (for the transfer rate) or a problem
> with the power supplies.

    What is the maximum?  6 m or something like that?  I should be
well within spec.

[much helpful description of panic messages deleted... thanks!]

> Well, my first guess would be the SCSI cable being 
> too long (or not good enough) or the peak load on the
> power supply being too high.
> 
> You can check the prior by using only slow transfers
> (async. or at most 5MB/s sync). If the power supply
> is at its limit, then you should be able to cause 
> failures by increasing the seek rate (ie. do random
> seeks with little data actually being transferred).

    Hummmm... what could I use to do that?  Running bonnie repeatedly
on the 4GB drive for the random seek tests?  I don't think there is a
way on the NCR (unlike the Adaptecs) to specify the bus speed or
sync/async mode.
--
Brian Tao (BT300, taob@io.org, taob@ican.net)
Senior Systems and Network Administrator, Internet Canada Corp.
"Though this be madness, yet there is method in't"




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