[4168] in linux-scsi channel archive
Re: Timeout errors with ncr53c895
daemon@ATHENA.MIT.EDU (Larry M. Augustin)
Thu Jun 18 13:04:54 1998
Date: Thu, 18 Jun 1998 10:02:47 -0700
From: "Larry M. Augustin" <lma@varesearch.com>
To: Gerard Roudier <groudier@club-internet.fr>
Cc: Oscar Fernandez Cantero <ofcantero@ceife.es>, linux-scsi@vger.rutgers.edu
In-Reply-To: <Pine.LNX.3.95.980617194800.476A-100000@localhost>
All the LVDS Fast-40 drives I know of (including the Cheetah and Atlas
III) do not have LVDS termination on the drive. To run Fast-40 Ultra2
with those drives you must be using a LVDS terminator at one end of
the chain.
The Symbios SYM8951U Ultra2 does have auto termination detection and
will correctly terminate one end of the SCSI bus. But you still need
a LVDS terminator at the other end of the SCSI bus. You can't
terminate on the Cheetah.
Both Quantum and Seagate told me this when we first began evaluating
Ultra2 drives. Quantum is confusing because the Atlas III *will*
terminate single-ended SCSI. But if you want to run the drive
reliably with Ultra2 you must disable termination on the drive and use
an external LVDS terminator.
Several companies make LVDS ready internal cables that have an LVDS
terminator already attached to one end of the cable.
Larry
p.s. Gerard - 53c896 manuals are on their way to you.
Gerard Roudier writes:
>
> On Wed, 17 Jun 1998, Oscar Fernandez Cantero wrote:
>
> > Hello SCSIers of the world,
> >
> > I have recently got a Symbios SYM8951U Ultra2 card with NCR53C895 SCSI
> > chip.
> > I use it with 3 Cheetah Ultra2 drives in a raid0 configuration.
> > I use kernel 2.0.34 patched with driver NCR53C8XX version 3.0 (the last
> > I think).
> >
> > When I use them in 20MHz mode (40Mb/s selectable in the setup utility of
> > the card)
> > all works fine. But when I try changing to 40MHz mode (Ultra2 mode) the
> > configuration
> > continues to be usable, but at arbitrary times an error arises that
> > suspends
> > the SCSI bus for a moment.
>
> Terminations is not the problem if you've attached a device at
> each end of the the SCSI BUS (the adapter is a device) and
> have enabled terminations on these devices only (The SYMBIOS
> Board uses auto-termination, but I donnot know about the Cheatah).
> BTW, a termination problem probably will break FAST-20 transfers too.
> Cabling is probably another story. There are some requirements for
> differential characteristic impedance and minimum spacing between
> stub connections that may break FAST-40 but not FAST-20 LVD.
>
> > The error says:
> >
> >
> > scsi : aborting command due to timeout : pid 186838, scsi2, channel 0,
> > id 2, lun 0 Read (6) 00 a5 48 30 00
> > ncr53c8xx_abort: pid=186838 serial_number=186870
> > serial_number_at_timeout=186870ncr53c895-0: abort ccb=013dd020 (cancel)
> > scsi : aborting command due to timeout : pid 186837, scsi2, channel 0,
> > id 1, lun 0 Read (6) 00 a5 48 36 00
> > ncr53c8xx_abort: pid=186837 serial_number=186869
> > serial_number_at_timeout=186869ncr53c895-0: abort ccb=06488820 (cancel)
>
> [ ... ]
>
> > This message sequence use to be repeated indefinitely.
> >
> > A few of the times it is able to continue, the most I have to kill the
> > process
> > associated to stop the messages.
> >
> > If someone could give some useful hints it would be very appreciated.
>
> You should check that the BUS cable is appropriate for LVD and should
> use a minimal spacing between devices of at least 0.30 meter.
>
> A device problem or a driver problem is not impossible, but checking
> that the BUS is ok is the first thing to do.
>
>
> Regards,
> Gerard.
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.rutgers.edu
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.rutgers.edu
