Does SCSI Ultra160 bus require termination for only one or two HDs?

[gba]

I accidentally purchased one single device and one dual device U320 LVD/SE cable, both without termination, to connect hard drives in two of my computers to Adaptec 39160 host cards in each. I picked out the cables from this page. It has always been my understanding that a SCSI bus was supposed to be terminated on both ends but since I had cables that could not be terminated, I figured that before I replaced them with the correct cables, I would experiment to see how my system performed without the terminators. Both have worked flawlessly. In one computer I have just the boot drive on the bus and in the other I have the boot drive and a scratch drive for audio/video work.

Will I be able to get away with just leaving things well enough alone or is it necessary for me to be terminating these buses? And if the buses must be terminated, for what purpose are the cables without termination sold?

Thanks in advance for any input people may have~

 

[RebateMonger]

I deal with SCSI drives off and on. So I'm hardly an expert at termination. But this "tutorial" says, "When do you terminate the bus? Always. Period. Whenever you want the SCSI bus to operate reliably!"

SCSI termination tutorial.

The last couple of Dell servers I purchased included a SCSI LVD U320 drive and a SCSI cable with five connectors - four for the drives and one terminator.

As far as cables without a terminator connection:
Maybe for devices that have a terminator built in? (Although that same tutorial says that LVD devices don't come with built-in termination).

 

[gba]

Thanks for the response, RM. Indeed, I am familiar with the tutorial you have linked.. I have read that you should always terminate in the Adaptec 39160 manual, as well.. that is what I was taught by my friend who got me into SCSI a few years back. I am just baffled as to why I have not had any issues.. and seeing as that I have only one and two HDs on the buses, perhaps it really does not matter that they are not terminated?.. and that could be why the cables without the terminators are sold, bc you can get away with using them in simple, short buses... and yes, it is my understanding that U320 requires terminators, that jumpered termination ended with, I forget, SCSI Wide, was it?.. the format that uses 50 pin connectors. But anyway, I decided to post to try to find out the answer to why the unterminated cables exist, since I have them here, they are working, and I do not feel like spending the money to upgrade them seeing as they are in older systems that I would like to just leave be... and, yes, I do realize all of this may just be a case of wishful thinking on my behalf.

 

[RebateMonger]

Years ago, I worked with lots of analog BNC cables/connectors that were always supposed to be terminated with a 50 Ohm terminator. I played with leaving the terminator off and didn't see any differences. But that was with analog data.

Many folks have probably experimented with 10Base2 cabling (thinnet). That also required termination and, to the best of my memory, appeared to also work fine without termination.

 

[gba]

ha, ha thanks for keeping my candle burning, RM... Hope springs eterna .. It is my theory that it is bc I am running short buses.. that is why I am getting away with it.. less data flying through the cable.. destined for different locations...