Date: Fri, 13 Aug 1999 21:33:53 -0500 From: David Kelly <dkelly@hiwaay.net> To: Karl Denninger <karl@Denninger.Net> Cc: Randy Bush <randy@psg.com>, FreeBSD SCSI <freebsd-scsi@FreeBSD.ORG> Subject: Re: dump to dlt gets write error Message-ID: <199908140233.VAA13520@nospam.hiwaay.net> In-Reply-To: Message from Karl Denninger <karl@Denninger.Net> of "Fri, 13 Aug 1999 19:16:46 CDT." <19990813191646.A57450@Denninger.Net>
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Karl Denninger writes: > I've seen this kind of stupidity before and you're not going to like the > problem or solution. > > Put the DLT on a different SCSI bus (different host adapter) from the disks. > > Specifically, separate the fast/wide and narrow SCSI devices. > > I've seen both DLTs and other "non-wide" devices have kittens with disks > running fast/wide on the same SCSI bus. It usually manifests itself as > an I/O error on the narrow device - which is exactly what you're getting. > > My guess is that the hardware on the narrow (and not-so-fast) device gets > mightily confused by the shorter signal times (even though they're not > aimed at that target) and randomly "freaks out" enough to botch an > operation. I'd go a bit in the other direction and ask, "How is the transition between narrow and wide being handled?" Specifically people tend to purchase "narrow to wide" SCSI cables and simply plug things up with narrow devices at the tail end of the SCSI bus. Narrow terminator on the far end, wide terminator on the SCSI card. Nothing in the middle terminating the high bits of the wide bus. There are special terminators made just for that purpose. I'd like to think problems are caused by the device having problems. But we're talking about electrons here, and those little guys are sneaky. It may very well be a wide device is causing the narrow device to have problems. You are supposed to be safe if the internal narrow devices are connected to the 2940UW on the narrow connector, and the wide devices are connected the same, as long as you don't put a Tee in your SCSI bus by adding an external device. Just because the 2940UW has 3 connectors doesn't mean you can use all of them at once. Another good way to deal with everything internal is to route wide cable everywhere but use wide-to-narrow IDC-like adapters right at each device. About $15 each. Don't use the narrow connector on the 2940. The external wide connector is still usable this way. An old used narrow Adaptec 2940, or Symbios '810, or a new Adaptec 2930, might be a very good solution for the tape and CDROM. -- David Kelly N4HHE, dkelly@nospam.hiwaay.net ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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