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Hanging SCSI BUS

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5 replies

by rickyd

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The system will not come up when a tape drive is installed. During the initial boot when the Scsi devices are looked at the system sees all of the devices to include the tape drive when it is installed. But after it reads the devices the next stepis that the prompt should say "SCSI BIOS installed correctly" however it hangs just prior to that. If it stays there long enough it attemps to boot from floppy saying that the disk drives are not bootable. All of the devices are addressed correctly and chassis positions have been changed with no help.

The workstation is an RPS with a Supermicro MotherBoard P6DGE with 1 GIG of RAM. Dual 500 Intel Pentium slot 1 processors, Adaptec aha-2940uw pro scsi host adapter. Mammoth exabyte 8900 tape drive (change twice). Ultra PLex CDrom and Plex writer CD-RW. Two 36 gig seagate hard drives.

5 replies

by james r linn

Check termination. The last device in a SCSI bus has to be terminated, and if you've changed the order it may have changed which device is terminating the bus.

If that doesn't work swap out cables.

In the bad old days(late 80s) we used to see some funky SCSI problems which had to do with certain combinations of devices. Douglas Adams(Hitchhiker's Guide to the Galaxy) wrote a great MacWorld article long ago about this very problem. He had 5 SCSI devices which would all work on their own, but not work together. He got shorter cables(sometimes helps), changed the order(sometimes helps), but in the end, he bought a different brand of scanner and voila everything was fine.

The explanation for this is that a SCSI bus passes power and a signal down the bus, and each device has to pass it along till the end, where the signal is terminated and turned around. Some devices don't pass along the signal as strongly as they receive it - so that by the time you get to the end of the chain, the signal is too weak. And some devices don't do the termination as well as they might.

Good luck.

James

by volkerk

In the SCSI controller's utilities (access by pressing Ctrl-A just before it discovers devices), check whether you can see all the devices under Disk Utilities. Check the host adapter settings, especially for termination. You may need to limit bandwidth on the devices or alter other device settings. Finally, and I guess this is your solution, on the 2940UW you can only use two of the three connectors. Two internal hard drives (I assume on the 68-pin connector) and two CD-Rom drives (likely on the internal 50-pin) mean that the external connector cannot be used. The only way to connect an external device is to get an internal cable with an external connector at the end, on a standard card bracket.

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