Adapting SCSI drives

[Heiroglyph]

I've got a lot of 68 pin SCSI drives, but all my controllers are 50pin.

I currently have one 50 pin cable, terminated on the end and the SCSI card terminated on the other.  In the middle I have a 50 to 68 pin adapter plugged into an unterminated 68 pin drive. (the plastic kind that attach directly to the drive, no extra cables or circuit board)

This seems good, but requires an adapter for every single drive and my local supplier is out of them.

Can I get away with one adapter at the controller (50 to 68), then a 68 pin cable with terminator?

Then every drive would connect directly to the cable and use just one adapter at the controller.

I tried this briefly but the drive wasn't recognized.  It could have been user error but it was getting late so I haven't tried again yet.

Thanks

[giZmo350]

Yup, you can do that. Just be sure to terminate the last drive in the chain and give each drive it's own ID with the jumpers on the drives circuit board.

[Heiroglyph]

After thinking about it, are you sure I won't need to unterminate the controller, then put a 68pin active terminator on both ends of the cable with drives and controller in the middle?

I have no idea if this adapter terminates the extra pins, but I severely doubt it.

Thanks

[giZmo350]

After thinking about it, are you sure I won't need to unterminate the controller, then put a 68pin active terminator on both ends of the cable with drives and controller in the middle?
 
I have no idea if this adapter terminates the extra pins, but I severely doubt it.
 
Thanks

The adapter(s) (connector adapters) shouldn't even come into play. If I understand you right, your going from a single SCSI drive to multiple drives using a single controller? When using a single drive it doesn't matter where the terminator is (controller or drive). But with multiple drives the controller has to be at the header end and the terminator at the last drive. Set each SCSI id on each of the drives themselves. Check here at Dave's SCSI school...
 
http://www.tracezero.net/SCSI/basics.php

[Heiroglyph]

Actually, there is no reason that the controller has to be in the middle, it's just another node.

I may have to work up a pic to explain the two options I came up with.

Those extra 18 connections in the wide cable worry me if they aren't being terminated. The controller wouldn't be attached to them, the drives would be.

[Zac67]

SCSI requires exactly two terminators at the ends. The unused connectors mustn't be terminated in any way.

[Jope]

But if you're using a wide cable, the entire width of the cable should be terminated.

So.. Have a cable with active terminators on both ends, disable termination from your HBA (scsi card) and all units. Then just plug everything in and you're all set.

[J-Golden]

Being a visual learner, I find explaining SCSI termination like a race track helps visualize the need and use of termination.

Imagine SCSI sends data only "one way" like a single lane road or on a race track.  The only way to get the data to "turn around" is to add a U-Turn.  That U-Turn is the terminator at one end on the cable.

Now that you have the data turned around, you need to get it to turn again to complete the circuit.  So you add ANOTHER U-turn/terminator at the other end of the cable.

Doing this allows the Data to race around (read/write) at full speed without slowing down because the U-Turns are made to redirect the flow without it slowing down.

Not putting on terminators causes’ confusion that then slows down data transfers, causes errors or even fails a drive that is working perfectly.  I've run systems without proper termination and believe you me; I have nothing but dumb luck to thank!

Someone mentioned terminating every unused spot on the cable.  Using the same analogy, terminating/placing a U-Turn will cause your data to turn around and go no further down the cable effectively cutting off any other devices connected past the terminator.

Hope this helps clear it up a bit.

[rockape]

Hi Heiroglyph,

See   http://www.wonkity.com/~wblock/SCSI/SCSIExamples.html

There are some diagrams which may help you.

Regards, Michael

aka rockape

[Heiroglyph]

But if you're using a wide cable, the entire width of the cable should be terminated.

So.. Have a cable with active terminators on both ends, disable termination from your HBA (scsi card) and all units. Then just plug everything in and you're all set.

That's what I was trying to say in my last post about the extra 18 wires.  It seemed to make sense.

I now suspect that my narrow to wide adapter is built incorrectly.  I found references on a FAQ about narrow to wide adapters that are wired incorrectly and ground out on older SCSI adapters.

It doesn't act like termination, it acts like the bus is just not there.  The drive isn't even spinning up.

[Heiroglyph]

Thanks for the examples, unfortunately all the examples I've ever seen assume the simple case of having all the devices on the same size attachment to the cable.

The tricky part here isn't the basic termination, it's the wide cable on a narrow controller.

For now I've just put a bigger 36GB SCSI drive on the 50 pin cable and I'll keep an eye out for other adapters or better still a wide SCSI controller.

Thanks

[Zac67]

Actually, the 'controller' (rather host bus adapter HBA) is just a SCSI device like any other.
(There's no 'bus master' in SCSI unlike IDE, USB, ... There's 'targets' and 'initiators' but these are just temporary roles that can change at times.)

If you look at it that way, you connect your wide devices (HDDs) with a wide cable, terminate properly, and adapt your narrow device (HBA) - that's it.

It's getting more complicated when you're building a SCSI bus that's wide for the first part (HBA, HDDs) and then gets adapted to narrow to connect older devices (CDROM, scanner). Then you'd need to use a 'half terminator' to terminate the upper byte while going narrow. Once I used a shared bus with an Adaptec 2940W at one end and my A3000 at the other with half termination in between. But no need to get more complicated here.

[Heiroglyph]

I think the thing that is causing the problem is a bad 50-68 adapter.

I'll break out the pinouts and a multimeter soon and see if that is the case and go from there.

This looks like what I have, although I can't be certain that it is wired exactly the same way: http://www.ramelectronics.net/computer-parts/scsi/scsi-adapters/scsi-adapter-adt-6850-ff/prodADT6850FF.html

I am plugging this into the HBA, connected to the middle of a wide (68) cable with terminators on each end.

[mechy]

I think the thing that is causing the problem is a bad 50-68 adapter.

I'll break out the pinouts and a multimeter soon and see if that is the case and go from there.

This looks like what I have, although I can't be certain that it is wired exactly the same way: http://www.ramelectronics.net/computer-parts/scsi/scsi-adapters/scsi-adapter-adt-6850-ff/prodADT6850FF.html

I am plugging this into the HBA, connected to the middle of a wide (68) cable with terminators on each end.

Your idea with a 68pin cable connecting the drives and a high byte adapter off the controller in theory should work. i have done this before,but using active termination on both ends is ideal i think in this situation. also beware of some UW multimode terminators on cables,they claim to support ultra160/320 and SE,but i find some don't live well with SE.Plain SE rated terminators are best. check pin 26(i think!) in the cable for term power,it needs to come from somewhere,only 1 device or the controller.

You need 68-50 adapters with high byte termination. this terminates the unused lines. most cheap adapters either don't do it or they ground the lines which doesn't always work. you either get unreliable scsi,only access to the first 4gb reliably or it simply hangs.

High byte adapters cost more but are the right way to do it.just terminate the ends of the bus as you would any scsi.

The one you list specifically says it has no high byte termination. They usually say it on the adapter if they are. like this:

http://discountechnology.com/68pin-50pin-SCSI-Adapter-with-High-Byte-Termination

-Mech-

[Heiroglyph]

On the bright side, I feel like the single drive set up I have is 100% solid.

1GB Sys: ~35GB Work:, both SFS and attached to the Warp Engine SCSI.  Gets over 9MB/s on diskspeed read and it's a 15K rpm drive, so access times are low for a spinning disk.  Something like 5.6ms according to Seagate.

I've copied tens of GB to it since yesterday and no lockups, errors or partition wraparound.  (I wrote a little script to just keep hammering it, copying data into a new folder each time)

Although I'd like to get a few more drives in it for redundancy, I'm not going to sweat it too much at this point.  I'll be backing up to a CVS or SVN server periodically once I'm all set up.