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SCSI Ultra Mode causes errors

Posted on 1998-08-17
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Last Modified: 2010-04-12
I just realized that my Adaptec 2940UW adapter has been running with the Ultra mode DISABLED, making the max transfer rate only 20MB/Sec.  The drive has been working fine for almost a year like this (what was I thinking).  Anyway...

I enabled the Ultra mode (40MB/Sec), and now, the drive (ST34371) doesn't work right, and I get errors reported when Windows boots, and it barely runs..freezing, unfreezing, like it's having negotiation problems.  

I went back into EZ-SCSI(CTRL-A) and disabled the Ultra mode (ouch), and now it works again.  The drive appears to be terminated properly.

The only other thing on the bus is a SCSI scanner (UMAX S-12), connected to the original 6' cable, with the adaptec 68-50pin adapter that terminates the unused pins.  Also, the scanner does have the terminator plug installed.  I thought I had everything right.  The internal cable is the original one that came with the drive (very short).

Any ideas?

Bill
:-=>
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Question by:Bigpaws
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Expert Comment

by:swwelsh
ID: 1123013
The faster the scsi bus, the more sensitive to cabling and termination problems. It could be that the scanner cable does not support the higher speed, since scanners are very slow compared to hard drives. Most scanners that I have seen tell you to set the adapter to 5mb/sec, and I have seen some scanner docs that mention problems with high speed controllers. I would try removing the scanner from the bus and then see if the ultra mode works. If so, maybe you could add a slower scsi controller to your system for the scanner.  I have mine on an adaptec 1510, and it works fine.
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Author Comment

by:Bigpaws
ID: 1123014
Well, Well, Well.  You're right.  I removed the scanner from the system and the drive works Great (Faster than ever).

Now, I guess I'll have to dig up that SCSI controller that came with the scanner and use that.  

Thanks!

Bill
:-=> (make yours the answer, above, and I'll credit you with the points (SWWELSH).
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Accepted Solution

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swwelsh earned 400 total points
ID: 1123015
The faster the scsi bus, the more sensitive to cabling and termination problems. It could be that the scanner cable does not support the higher speed, since scanners are very slow compared to hard drives. Most scanners that I have seen tell you to set the adapter to 5mb/sec, and I have seen some scanner docs that mention problems with high speed controllers. I would try removing the scanner from the bus, and then see if  the ultra mode works. If so, maybe you could add a slower scsi controller to your system for the scanner. I have mine on an adaptec 1510 and it works fine.
 
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