On Friday 04 February 2005 10:12, Geert Uytterhoeven wrote:
>On Fri, 4 Feb 2005, James D. Freels wrote:
>> The tape drive is within the VXA-2 Packet-Loader 1U rack mount. 
>> It is connected via an external
>> scsi cable that came with the drive.  the unit also came with it's
>> own terminator which is also plugged into the
>> packet loader.  The packet-loader is the only device connected to
>> the scsi card externaly.
>>
>> Inside, the scsi card has both a scsi-1 and scsi-2 connector.  The
>
>You mean, a narrow and a wide connector?
>
>> scsi-1 connector has a single device
>> connected (the CD-Rom).  The scsi-2 connector has the rest of the
>> devices connected on a single cable
>> (3 hard drives, 1 VXA-1 Exabyte tape drive).  It is a fairly long
>> cable, with about 8 inches of cable separating each
>> device.  The last device on the cable is the VXA-1 tape drive
>> followed by a termination on the cable itself.
>
>So the cabling is your problem: you should use maximum 2 of the 3
> connectors on a SCSI card, since it's supposed to be a single long
> chain without branches.

Said another way, that card may well have the narrow connector in 
parallel with the wider one, and if thats the case, serious term 
problems are in store.  FWIW Geert, all 7 connectors on a given cable 
can be used, provided the terms are removed from every device but the 
last one, and the last device is truely on the end of the cable.  And 
the term power supplied is up to specs.  The 4.3 to 4.4 volts you get 
by way of the average cards isolation diode isn't spec by the .6 
to .7 volts missing due to that isolation diode.

Now, where both the internal connectors on the card and the external 
connector are in use as this person indicates, then the card, which 
may have automatic terminations, must terminate ONLY those lines of 
the wide bus that do not go on out via the rear panel connector to 
any narrow devices at that end of the cable.  The card, as far as the 
original 8 bit data bus portion of the 50 pin cable, effectively 
becomes a wired or device in the middle of the transmission line and 
must not terminate those lines.  I'm not fam with this card, but most 
of the cards have an either/or term control, effectively rendering a 
lashup such as is being described here, pretty much unworkable.  My 
best card was that advansys, and it did not have the ability to 
terminate just the high order lines, which is what would be required 
here.

I'd recommend strongly that this person get another scsi card, and put 
the tape drive on it by itself, so that he has all the internal 
devices on one card, and the external device on the other.  Life will 
be simplified considerably.

>It's the same on mine (I have one with internal narrow and wide, and
> external wide connectors).
>
>Gr{oetje,eeting}s,
>
>      Geert
>
>--
>Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> geert AT linux-m68k DOT org
>
>In personal conversations with technical people, I call myself a
> hacker. But when I'm talking to journalists I just say "programmer"
> or something like that. -- Linus Torvalds