Date: Fri, 28 Nov 1997 12:06:42 -0800 From: David Greenman <dg@root.com> To: jack <jack@diamond.xtalwind.net> Cc: freebsd-isp@freebsd.org Subject: Re: Adaptec 2940 and FreeBSD 2.2.2-RELEASE Message-ID: <199711282006.MAA19602@implode.root.com> In-Reply-To: Your message of "Fri, 28 Nov 1997 14:55:14 EST." <Pine.BSF.3.96.971128144614.1044B-100000@germanium.xtalwind.net>
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>On Fri, 28 Nov 1997, David Greenman wrote: > >> >On Fri, 28 Nov 1997, Jeff Lynch wrote: >> > >> >> The only problems I've had with 2940UWs on fbsd2.1.5-2.2.1 have occurred >> >> when we mix wide/narrow devices on the host adapter or attach a narrow >> >> (of course) external tape drive. Leaving the bus all wide or all narrow >> >> and all internal has never given us problems. >> > >> >The servers we have that keep blowing up have only a single internal DAT >> >on the narrow bus and a single internal UW HDD on the wide bus. It most >> >common for a tape error to lock up the machine, but they also lock up >> >with the same symptoms when no backups are being done. >> >> Hmmm...Do you have a narrow->wide converter than has termination for the >> upper (wide) data bits? I had a lot of problems here with using a narrow >> drive on a wide controller until Justin pointed out that the upper bits have >> to be terminated. I fixed the problem by putting a wide device at the end >> of the same cable that the narrow device was on (thus providing full wide >> termination). > >The trick, I think, is to have the last wide and the last narrow devices >terminated. On the controller do not terminate the narrow but do >terminate the wide. Works out something like this: > > >W---------------C >I O >D N >E---------------T >N---------------r-------N >A o A >R l R >R---------------r-------R > >Not quite up to Terry's ansi art but you get the idea. :} > >Note that you can only use two of internal narrow, internal wide, and >external. Using all three results in a 'Y' effect on the narrow side of >the scsi chain. That would terminate the narrow portion in the middle of the cable for one end of the termination. Termination needs to be at the physical end of the cable in order for it to work correctly. For people who need to put a narrow drive on a wide SCSI bus, there are available special wide->narrow converters that provide termination for the upper data bits - they're quite a bit more expensive, however. -DG David Greenman Core-team/Principal Architect, The FreeBSD Project
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