[5175] in linux-scsi channel archive
Re: Termination questions
daemon@ATHENA.MIT.EDU (Harvey Fishman)
Thu Nov 19 04:54:47 1998
Date: Wed, 18 Nov 1998 13:49:53 -0500 (EST)
From: Harvey Fishman <fishman@panix.com>
To: Steven Saner <ssaner@southwind.net>
cc: linux-scsi@vger.rutgers.edu
In-Reply-To: <19981117141548.D3132@jasper.southwind.net>
On Tue, 17 Nov 1998, Steven Saner wrote:
> I have what might be an elementary scsi question. I have a lot of
> hardware and electronics background, but I am new to scsi.
>
> I have an HP 5000i SureStore DAT drive and a Mylex BT-958 card. I also
> have a 50 pin ribbon cable to connect the two. My question is, do I
> need a terminator at the opposite end of the cable from the
> controller.
>
> The controller is auto-terminating, so it will take care of its end of
> the bus. According to its documentation, generally the device you are
> connecting it to will have built in termination that can be enabled or
> disabled. The tape drive documentation, however, does not indicate
> that it has internal termination. It suggests that you will need to
> put a terminator on the cable if the tape drive is the only, or last device.
>
> A friend of mine told me that some of the newer cards would not
> require such a terminator and that I should try it without. I have not
> yet done that, but I wondered if someone has experience with this
> and could shed some light on it.
Auto-termination is for the Windows 95 set and is about as reliable as
Windows 95. Turn it off and configure the card to have the termination
definitely on using the configuration program. The SCSI bus is a
transmission line, and if not properly terminated at each end you will get
reflections that could easily interact with data signals on the line
causing errors in the interpretation of the data. With only a single
device other than the terminated host adapter on the bus, the probability
of an echo conflicting is less, but "Hey, its your data. How much is it
worth?" Seems to me that if you are spending the time and effort to back
up the data with the tape unit, it is pretty silly to take chances by not
spending the extra few dollars for a good external terminator.
Harvey
----------------------------------------------------------------------------
Harvey Fishman |
fishman@panix.com | A little heresy is good for the soul.
718-258-7276 |
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