SCSI question

[dunbar]

I recently purchased 4 Seagate Elite 23 drives (ST423451W), and I learned from other forums that the drives 68 pin SCSI-3 wide interface would fall back to original SCSI by using an adapter. So to adapt from 68 pin SCSI wide to the old Macintosh 50 pin internal SCSI, simply get the correct genders, and all is fine. Except, I learned, that some adapters will block access to the power connector....

So, before I bought any adapters, I contacted one online merchants tech support department about the adapters which they offered. In their response, they mentioned that I should get an adapter with 'High Byte Termination'. I was a bit surprised that any hard disk drives 'built in' terminations would not properly address all configuration issues. My emailed response to the techs recommendation asked what is 'High Byte Termination' but the message has been ignored (only one techsupport email per customer, I guess).

So, naturally I tried the disk drives manufacturer, Seagate, and their tech support person kindly offered that the 18 unused data lines were the high bytes. But Seagate never mentioned needing to terminate the high bytes. The Seagate drive manual seems to skip this topic as well.

Any ideas as to my dilemma will be kindly accepted.

[Ming]

High byte termination is well covered in the faq located here:
http://www.cablemakers.com/scsitermination.htm
I can't say much about the Seagate ST423451W drives, as I have had a few, and the power adapter for the drive is in the way for most cheap adapters. By the time you get an adapter that works and the cabling, it seems it is cheaper to buy a different drive. Well, that and the drive seems to put off a lot of heat. As far as adapters that do work, I have one that works incredibly well, an A-tec 80 pin SCSI adapter that had 50 and 68 pin connectors with jumpers for high byte termination if needed. Unforunately this was a few years ago, and am not really sure where you can find them now.

Edited to add:
The adapters look much like the ones here:
http://www.scsi-cables.com/sca-adapt.htm
Specifically the ADP 9022, except it has jumpers for termination. The site also has other scsi adapters, but none that run 50 pin male, to 68 pin female with high byte termination. If you see one, they are about the best because you can just connect the 50 and 68 pin cables without worrying about an adapter for every drive.

[dunbar]

Ming - thank you for the links, I will investigate the adapters they offer, and the faq is good to have on hand.

The one disk drive at which I looked (I bought 4 of them) had holes for the data connector, that connection is defined as a female, yes? If so, I would need a male connector in order to mate to the drives data connector. The 50 conductor ribbon cables I use all have holes, those are females as well. From that information, I need a male 68 to male 50 adapter.

Regarding termination, the specifications for the drive proclaim that the drives have active termination built into them, and that I can disable the active termination via a jumper or two.

Would that drive still need external termination? The drive termination is before the adapter, so IMO, the adapter wouldn't need to supply termination at all, unless I missed something along the way.

I was thinking about using this (http://www.scsisource.com/scsi_adapters/internal_scsi_adapters/) company for their adapters, they look like a bit less $$.

[Ming]

The prices listed on the company you mentioned do look very affordable. As far as the connectors, I should have been more specific. The ST423451W does have a 68 pin female connector on the drive. What I was thinking of for hooking up the drive(s) was have a short 68 pin cable run off the drive to an adapter. Then hook up the 50 pin cable to the adapter. Regular 68 pin cables have male connectors, so I was thinking one would link a 68 pin cable to the 50m to 68f adapter with high byte termination, then link that adapter to the 50 pin cable running to the scsi card. If you look at the 50M to 68M adapter, the 50pin portion of the adapter runs over the power plug on the drive.

Edited to add:
In regards to termination, the drive should still be providing active termination. At least the last one on the cable should be anyway.

[Xaotic]

Narrow chains will severely limit your performance to around PIO mode 4 equivalent(fast SCSI is 20MB/s). It'd be better to get a wide cable based adapter(68 pin) and a 68 pin cable with termination since your drives are already 68 pin and faster han narrow SCSI. Unless you are using it on an older MAC.

[dunbar]

Originally posted by Xaotic
Unless you are using it on an older MAC. For 3 of the drives, yes, installing into a Quadra 950. The 4th drive will hopefully fit a Dell Precision 410 workstation I'm about to resurrect.... might not fit the case, though.

[dunbar]

Originally posted by Ming
In regards to termination, the drive should still be providing active termination. At least the last one on the cable should be anyway. I was intending to apply the same rule I used for 50 pin SCSI systems (used the rule on older Macintoshes): 'terminate only the ends of the chain'.

That should still be true for 68 line SCSI (correct me if I'm wrong).

My most major concern, ultimately the purpose for this thread, is based on the 50 to 68 conversion... if the hard disk drive is doing the terminating, I'm assuming the drive will be correctly designed to properly terminate all 68 lines; low bytes as well as high bytes. Thus, if the disk drive is performing the termination, my understanding is that my adapters should not NEED termination capability in any position on the 68 pin SCSI bus, not at all, unless I re-use the adapters with a drive that does not terminate the bus at all.

Unless...... does the drives databus actually 'see' the 2 terminations (termination of the opposite end of the bus, as well as its own termination)? If that is true, then the high byte termination functions will emulate the controller termination of a 68 line SCSI system which is terminated at the far end as well as at the adapter.

Again, I appreciate all the help.

[Xaotic]

Largely, the same rules apply. Termination is only at the ends of the cable. Some information is here, but incomplete.

http://adaptec-tic.adaptec.com/cgi-bin/adaptec_tic.cfg/php/enduser/std_adp.php?p_sid=m4jYIPRg&p_lva=&p_faqid=9&p_created=925342076&p_sp=cF9zcmNoPTEmcF9ncmlkc29ydD0mcF9yb3dfY250PTIyN SZwX3NlYXJjaF90ZXh0PTY4IFBJTiA1MCBURVJNSU5BVElPTiZ wX3NlYXJjaF90eXBlPTMmcF9wcm9kX2x2bDE9fmFueX4mcF9wc m9kX2x2bDI9fmFueX4mcF9jYXRfbHZsMT1_YW55fiZwX3BhZ2U 9MQ**&p_li=

Here is the correct listing of what you need to do:

Follow the link, scroll down to the Table of Contents and then find the link stating "Can I connect a WIDE device to my narrow SCSI host adapter? "

http://scsifaq.org:9080/scsi_faq/scsifaq.html

Basically, the adapters should handle blocking the high bits and enable proper function. The link has a listing of adapters which have been proven to work.

[dunbar]

Originally posted by Xaotic
http://adaptec-tic.adaptec.com/cgi-bin/adaptec_tic.cfg/php/enduser/std_adp.php?p_sid=m4jYIPRg&p_lva=&p_faqid=9&p_created=925342076&p_sp=cF9zcmNoPTEmcF9ncmlkc29ydD0mcF9yb3dfY250PTIyN SZwX3NlYXJjaF90ZXh0PTY4IFBJTiA1MCBURVJNSU5BVElPTiZ wX3NlYXJjaF90eXBlPTMmcF9wcm9kX2x2bDE9fmFueX4mcF9wc m9kX2x2bDI9fmFueX4mcF9jYXRfbHZsMT1_YW55fiZwX3BhZ2U 9MQ**&p_li=Link didn't work, and even when I truncated down to the base URL, site timed out. Will try later, in case of internet chokage.

http://scsifaq.org:9080/scsi_faq/scsifaq.html

Basically, the adapters should handle blocking the high bits and enable proper function. The link has a listing of adapters which have been proven to work.
Lost. I believe that adapters will 'block' the added 18 lines, but since the drive terminates its own end, I still do not know why the adapter needs the high byte termination... the faq saysAnother purpose served by the hi-9 terminator is supplying pull-up current to the upper data lines which would otherwise be left floating.I'm still thinking that is a moot point since the drive provides termination for 68 line SCSI, so why do I need the added termination in the adapter when the drive terminates the upper as well as the lower???? Just lost, I'm simply not getting that clear in my head.

[Ming]

A good way of looking at high byte termination is that it only is necessary for SCSI wide devices hooked up to a Narrow SCSI channel. Terminator power would be required of the drive whether or not it was 50 or 68 pin as long as it is at the end of the chain. The last device on the chain needs termination power. Termination power is not related to high byte termination, which basically allows a wide channel device to be used by a narrow channel controller. If a 50 pin cable was hooked up to a 68 pin cable using an adapter, and the controller was was a FW or UW controller, there would be no need for high byte termination (at least I haven't had any problems connecting 50 pin devices to a 68 pin controller). The problem is the reverse, Wide Channel devices being used for a narrow channel controller. If you have 3 of the ST423451W drives being hooked up to a narrow channel controller, you only need one adapter to run the 68 pin cable off the 50 pin cable. The adapter would need to provide high byte termination, and it would do so for every device hooked up to the 68 pin cable. The last drive on the chain would need active termination. Not sure if that helps.

[dunbar]

Originally posted by Ming
The problem is the reverse, Wide Channel devices being used for a narrow channel controller. If you have 3 of the ST423451W drives being hooked up to a narrow channel controller, you only need one adapter to run the 68 pin cable off the 50 pin cable. The adapter would need to provide high byte termination, and it would do so for every device hooked up to the 68 pin cable. The last drive on the chain would need active termination. Not sure if that helps.
Maybe I'm looking at this all wrong.

For the Dell 410, I have a terminated cable, so that box is not a concern (provided I terminate everything correctly).

For the Macintosh Quadra 950 box (SCSI-1 or 2), I have a spare 7 position 50 conductor SCSI ribbon cable to use for the 3 drives and I was considering installing one adapter at each of the 3 drives.
At about $22 each including shipping, that is $65ish, and I'm reusing the 50 conductor cable, with 3 adapters.

At present, I do not own a spare 68 conductor SCSI cable to use for those Macintosh drives. The 68 conductor cables prices which I last saw were nasty as all get out, over $100, but I'll go look again using the new links above.

If the cables are less than one adapter, then I think I see how your configuration makes more sense...

EDIT: yes, I guess the cable is a lot cheaper than I had in mind.... will be rethinking my plan, thanks to Ming for the tip! /EDIT

[Xaotic]

If you need stuff, I have some older legacy SCSI stuff collecting dust. I'll have to test some cables, but I should have at least one 68pin SCSI2 LVD with termination and a spare working AHA-2940UW(only does 20MB/s, shoud do 40MB/s, but I just tested it for function) with 50 and 68 pin interfaces. If you think you can find MAC drivers for that card, I have 2 controllers. Yours for shipping cost. I'll be doing some equipment testing this weekend.

[dunbar]

Originally posted by Xaotic
If you need stuff, I have some older legacy SCSI stuff collecting dust. I'll have to test some cables, but I should have at least one 68pin SCSI2 LVD with termination and a spare working AHA-2940UW(only does 20MB/s, shoud do 40MB/s, but I just tested it for function) with 50 and 68 pin interfaces. If you think you can find MAC drivers for that card, I have 2 controllers. Yours for shipping cost. I'll be doing some equipment testing this weekend. Thanks for the offer about the card, Xaotic, but the Mac I'm working on is NuBus based, very old Mac expansion bus; it has onboard SCSI-1. As for the cable, I'm still not totally clear about which way I will go, I'm still thinking that I may adapt the 3 drives down to match my 50 conductor cable. The 4th drive will go into the Dell 410 which has 68 pin SCSI and will actually use the drive to its limit.