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

[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

[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.

[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

[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.

[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.

[Heiroglyph]

So Heiroglyph, with all those parts you finally have one solid, reliable system?
Wow, you put in a lot of work, but at least you're probably more familiar with your hardware now.

Finally!

I'm still trying to get one of the 060's in there and I'd really like one of the 4000T's working, but at least I've got one system that works well.