backplane identification

[Doug Russell]

On Mon, 20 Sep 2004, Charles Sprickman wrote:

> On Thu, 16 Sep 2004, Justin T. Gibbs wrote:
>
> Interesting.  Saturday we went in to replace all 4 18GB drives with 36GB
> models.  While I was in the box, I recabled so that the chain went in one
> backplane, and then to the other with a seperate cable.  Also put a
> terminator on the second backplane's "end" of the chain.  With the
> terminator on, no drives were found by the controller.  With the
> terminator removed, 4 drives showed up, but one would always show a sync
> rate of 80MB/s vs 160MB/s on the others.

You're sure the backpanes have no built-in auto-terminator, and that the
terminator you are trying to use is the correct type of terminator for the
bus.  (You're using a standard LVD-style terminator, not a HVD...)

Sounds like either a total length problem (add up the length of your
cables, and add the electrical length of the backplane cards' bus traces).
Are you within the specification for U160?  (I don't recall exactly what
that is off the top of my head, but if you're ending up with double the
cable length you're supposed to be 'allowed', then you're probably running
into timing problems due to the length of the bus.)


> wonder if perhaps the whole mess is not new enough to support UW SCSI @
> 160MB/s?

Possible.  If the length is okay, it may be that the backplane design
just isn't built for 160 and you get crosstalk, etc between lines at the
high frequency.  Things should be found if you force the controller to 80
in this case, though.

> Last question...  Are the layouts of these SCA backplane cards at all
> standardized?  I'd gladly swap these out for anything that included docs

Not likely.  :(

Later......						<Doug>