LVD scsi external connector cabling problem, shared segment cable problem Ultra2 U160 U320

 

 

The Ultra2/U160/U320 SCSI external connector problem


So, you have a lovely new Ultra2/U160 SCSI card in your computer. 80 MBps! Baby! But wait! You need to hook up an external scanner/Zip drive/Jaz drive! Can you just plug it in???!!! Well, you read the manual, but still don't have a clue? You are not alone!!!


The External connector problem

Most Ultra2/U160 adapters use the same "segment" for the internal Ultra2 and external connector. Why? Possibly for the people who want to use an external box for their Ultra2 SCSI Hard drives in software RAID configurations or possibly, because they want you to buy internal/external adapters from them, or possibly because they are morons. Ok, ok, they couldn't possibly be morons!

You can connect non Ultra2 devices to it, with no problems, except that the maximum throughput of your Ultra2 segment will be limited to 40MBps (Ultra Wide SCSI) speeds! Also, now that you are basically running Ultra now, instead of Ultra2 you should know that "Ultra" SCSI cable lengths are severely limited! The maximum cable length is ten feet when four devices (including the host adapter) or less are on the bus. If five devices are used (four devices and your host adapter), then the maximum bus length is 1.5 meters (five feet!). You probably shouldn't get overly paranoid about the speed part, since there isn't a single hard drive alive that can come anywhere even close to 40Mbps anyway. If you want to add more drives in the future, especially "striped" drive sets, want long cables, or just like everything as Maxxed out as possible, then you will want to use the SCSI-2 connector on the SCSI controller card, (if it has one) to run a cable (APF-38005) to an internal/external adapter (ADT-21114) , and use that "segment" instead of the provided external connector.

If you don't mind the "possible" performance "hit", then go ahead and use that external connector!!!

Yes, I know this is very confusing!

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SCSI cable Length guide



 Thomas Steves