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Subject:
Re: SCSI Termination and cabling
From:
Bill Cohane <[log in to unmask]>
Reply To:
PCBUILD - Personal Computer Hardware discussion List <[log in to unmask]>
Date:
Sun, 12 Jul 1998 00:03:58 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (58 lines) 
At 18:24 11-07-98 +0100, Jim Gemeinhardt wrote:
>I recently had to replace a failed drive on a  2- Quantum 4.3G SCSI
>drive Windows NT server.
>Disk 0 - Quantum 4.3G scsi drive (working fine)
>        First physical drive on controller card
>Disk 1 - Quantum 4.3G scsi drive (failed)
>        Second physical drive on controller card
>The Adaptec 2940UW controller was configured as follows.
>Device #0 - Disk 0 (also the boot disk, I THINK it is terminated)
>Device #3 - Disk 1 (not terminated)
>Device #7 - Adaptec 2940UW controller card (terminated)


Hi Jim

The SCSI ID (for example, the numbers 0, 3, and 7 above) has no
relationship to a device's position along the cable and it does
not determine whether the device should be terminated or not.

The last device on the cable should be terminated. (Since your
controller is at one end of the cable, it too must be terminated.)
Sometimes, terminating the wrong device or terminating extra devices
seems to work but it is unlikely that the resulting setup would be
completely stable. Something inevitably will go wrong at an inopportune
time.

>Device #3 is attached to the third connector on the chain, it's also
>the last device on the chain, should it be terminated?

Yes!

>If I terminate Device #3 then Device #0 will be in the middle of the
>chain. Will Device #0 still be shown as Disk 0?

Yes!

>The device order on the cable will be #7-Controller (terminated),
>#0 Disk 0 (not terminated), #3 Disk 1 (terminated).
>a. Will this work correctly?
>b. Do I need to change the Device number order to be #7, #3, #0?

(a) If there are no other problems, this setup should work correctly.
(b) There would be no reason to change the order of devices.

>The current setup is
>Device #7 - controller (terminated),
>Device #0 - Disk 0    (terminated),
>Device #3 Disk 1 (not terminated).

This is wrong and you are lucky that you can see Disk 1.

You did not mention whether your disk drives are wide devices (that is,
have 68 pin connectors). I assume tht they are. If not, there are other
factors that must be considered.

Regards,
Bill

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