At 09:45 1/22/2000 , Brad Loomis wrote:
>[Adaptec says]:
>"When two or more SCSI hard drives are attached to the SCSI
>controller, SCSI
>Select intermittently sees the hard drives but FDISK returns 'No Fixed
>Disk
>Present' when executed.
>
>"This information applies to...2940 series...CI SCSI Card(s)...
>Most hard drives have an option for Termination Power (often labeled
>as 'TP'
>or 'TermPWR'). If the hard drives that you're using have jumper
>settings for
>Termination Power, then verify the jumpers are set to:
>'Disabled' or 'Receive Termination Power from SCSI bus.'
>
>"Adaptec's ISA and PCI SCSI controller cards provide termination power to
>the SCSI bus. If one or more devices also set to provide Termination Power
>to the SCSI bus, then the devices may not be detected normally by FDISK."
>How can I resolve this?


Hi Brad

My initial recommendation to have termpower supplied by the host adaptor
alone should not cause any problems on a SCSI bus with a *total* cable
length of 5 feet or less and active termination at both ends. This
distance is short enough that the termpower voltage as set by the
adaptor should not noticeably drop toward the end of the bus. And
since you have only three drives on the SCSI bus (you haven't added
anything have you?), there should not be too great of a capacitive load
on the bus. (The more the capacitance, the more the impedance of the bus.
Think of impedance as being analogous to resistance. Then think of
resistance as lowering the voltage that is needed at the end of the bus
to run the terminator. And the terminator keeps all the other lines
on the bus at the correct levels.) Increasing the total capacitance
of the bus increases the "effective" length of the bus. (By effective,
I mean not the actual length but the length as perceived by the adaptor.)

I suppose it's possible that having the drive supply its own termpower
could also supply termpower to the bus...and cause the problem described
by Adaptec. But that would surprise me since there is also a setting to
have the "drive supply termpower to the bus". And that setting would
imply that the drive gets its termpower from the bus. (Since there is
also a separate setting for "drive gets termpower from the bus". That
seems redundant.) Since there is no easy way to tell, I'd suggest
setting termpower "from the bus" (that is, from the 2940UW adaptor)
and see if it helps solve your problem.

It still seems to me that your problem is something different. I'll even
go so far as to say that thinking you have a bad hard drive is grasping
for straws...at this point anyway. There are too many other more likely
possibilities for you to go thinking of sending your drives back.

Regards,
Bill

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