termination and cabling question

[Desmond A. Kirkpatrick]

Sheldon,

> On Net Express' web site there is a statement about the need to have a
> linear topology instead of a branching topology for the cabling. They
> suggest that all devices should be on the same cable, so that, e.g. one
> should have
> 
>   tape -> contoller -> internal scsi disk -> internal cdrom)
> 
> Mine is 
>   tape -> controller -> internal scsi disk (all 68 pin connectors
>              |
>             \ /
>           50 pin internal cdrom
> 
> For the first setup, I would need an adaptor since the internal disk is
> 68 pin and the internal cdrom is 50 pin. 
> 
> It is working as is.  In private e-mail, they suggested that this is not
> scsi compliant and may lead over several months to damage to the
> hardware.  
> 
> I am seeking other opinions and/or experience.
> 
> Would it help to put an active terminator on the end of the external
> tape drive?   Is it really better to simply get the adaptor for the
> internal 50 pin connector? 

I have the same situation and I ended up buying the internal 50-68pin
adaptors.   The reason is because while everything seemed to work, my
tape drive would not stream properly (it would 'hunt' on long files
while backing up).  One day, when repartitioning a disk, I found that
one of my archives was corrupt.  I did a lot of testing and found that
improper termination (anything not linear on the chain), and even
attaching a SCSI-1 ZIP drive on the external cable caused the
corruption (I could actually repeat it if a long file was backed up!)

I also found it was quite easy to confuse the autotermination with
funny cabling (SCSI-III to SCSI-II to SCSI-I).

The fact that I saw NO warnings in the logs makes me extremely careful
about SCSI termination.  Especially while doing backups, make sure you
are in a KNOWN-GOOD termination situation (e.g, I remove my ZIP when
backing up).  The _only_ evidence I had of questionable termination in
either situation was a tape drive that didn't quite stream and
intermittent corruption.

The unfortunate part of all this is that those internal connectors are
expensive, almost as much as an external cable.  They seem to be
getting cheaper and easier to find, however.

OS: Linux v2.0.31,  PPro-166, Sony 7000 DAT, Quantum AtlasII

Desmond Kirkpatrick