SCSI cable question

[sm8000]

Is there such thing as an external SCSI cable with one end being 68-pin male, and the other end 50-pin male Centronics? Or would this be possible through a cable-and-adapter solution?

[BipolarBill]

http://shopper.cnet.com/4014-3101_9-1742076.html?tag=ob_50&orderby=50&sort=asc

[sm8000]

Beautiful! Thanks very much! :t

[Peter M]

Note that such a cable must contain termination for the upper half of the Wide databus on its 68-pin end.

[sm8000]

Thanks for the info. If I have the 68-pin end plugged into my card's external connector, the card will terminate it, right?

[Peter M]

No. That's because the card just sees _something_ connected, without being able to judge whether it's wired Wide or Narrow.
Wherever you transition from Wide to Narrow, you need to terminate the dangling Wide end.

The host adapter can manage that itself only if the Wide/Narrow transition takes place on the host adapter itself - e.g. when you use both the Narrow and Wide connectors of the same channel.

Also note that all Narrow equipment inherently is not LVD, and will kick your SCSI channel back to single-ended operation with a maximum speed of 40 MB/s (wide) or 20 MB/s (narrow).

That's why dual channel adapters are a good idea. Told ya ;)

[sm8000]

I do have a dangling wide end (that sounds sooooooo wrong!) and a plug for it which I'm betting will terminate.

The device on the Wide end, however, will be (presumably) Narrow - either this (http://sdd.toshiba.com/main.aspx?Path=/818200000007000000010000659800001516/8182000000e5000000010000659c00000d07/81820000002e000000010000659c00000362/8182000005f6000000010000659c0000132d) , this (http://sdd.toshiba.com/cda/main.aspx?Path=/818200000007000000010000659800000001/8182000000e5000000010000659c00000d07/81820000002e000000010000659c00000362/81820000003d000000010000659c0000011c) , or this (http://www.pioneerelectronics.com/pna/product/detail/0,,2076_17573129_37517,00.html) (I'm sure Pioneer may have a few others!) What I want to connect to it is a small 68 Narrow to 50 Wide adapter plug, then the 50 pin Centronics connector connects out to the cable I'm looking for, which goes 68 pin Narrow into my card.

In this setup, will the SCSI speed change over the different media? Also, am I still risking the fallback to SE mode?

Thanks very much for your advice. :t

[BipolarBill]

How many channels do you have? If you have two and there's nothing else on the external channel, it really doesn't matter.

[sm8000]

Just one, it's an LSI U160 - I got the Hypermicro deal with the IBM drive last Christmas ('02). I'm only getting around to setting it up now - don't ask.

[BipolarBill]

Urm - it's gonna choke the IBM drive. :(

[Peter M]

They're all single ended. That'll kick the entire SCSI chain back from U160 to UW(40). That'd choke the HDD even if there were nothing else on; while the DVD drive runs, the HDD will be even more choked.

If you're going with a 50-68 adapter plug and a 50-50 cable, then that adapter will have to terminate the upper half of the bus. No excuses there.

I did tell you waaaaay at the beginning that you better get a dual channel SCSI adapter if you intend to run other SCSI stuff besides HDD, didn't I?!?

Tekram's 390U3W and LSI's own 21003 are your friends. They have one U160 and one dedicated UW40 channel, and both come with an external 50-pin connector, btw.

Or better yet, get an IDE DVD drive. As long as you keep it on a cable of its own, there's not much wrong in doing that. Their SCSI versions aren't better at anything, not even sturdier. Those days, sadly, are over. It used to be different. No I'm not selling you my Yamaha burner, and the 5-CD changer isn't for sale either ;)

[sm8000]

Originally posted by Peter M
That's why dual channel adapters are a good idea. Told ya ;)

Originally posted by Peter M
I did tell you waaaaay at the beginning that you better get a dual channel SCSI adapter if you intend to run other SCSI stuff besides HDD, didn't I?!?

Honestly, I don't think that was me. I sure don't remember it, either in posts or PMs. Maybe it was though.... oh well. Anyway, thanks for sharing the knowledge. This adapter (as well as the drive) was free, a Christmas gift, so I'm just trying to make the best of what I've got. Time to revisit the drawing board.

[BipolarBill]

Well, you could add another SCSI card and disable the boot ROM.

http://www.newegg.com/app/ViewProductDesc.asp?description=16-123-101&depa=0

You won't need the adapter either.

[sm8000]

Man, you're a fountain of good ideas lately! Thanks :t

[Peter M]

If you add another, then use an LSI 20860 (or the older 8600). These don't bring a boot ROM at all, are just as cheap as that ACARD thing, and have the same quality drivers as the U160 card. And with the U160 card bringing a universal LSI SCSI boot ROM, the little card will magically become bootable too since the big one's ROM will adopt it as a secondary channel. Tekram also had a "310U" card that used the same LSI 53C860 Ultra-SCSI chip.

That ACARD thing is just awful. Stupid chip (high CPU load), poorly maintained drivers. Just. Don't.
For the same reasons, skip the temptingly cheap Tekram 315/395 series. These use Tekram's own attempt at building a SCSI chip, not LSI's good ones.

[BipolarBill]

It's really hard to find either the LSI or Tekram here, Peter.

[sm8000]

True, pricewatch can lead you nowhere. But Froogle (http://froogle.google.com) can be your friend!

http://froogle.google.com/froogle?q=LSI+20860&scoring=p

[BipolarBill]

http://www.wellspent.org/Product?p=218171

Well there you are! Froogle stomps Pricewatch, apparently. :r

[sm8000]

Peter - my 20860 arrived today :) Still waiting on the new mainboard. Meanwhile I wanted to ask about a different card. I was hoping to get one with the 50-pin connector on the outside (this one has 68). What would you recommend that will be adopted as my U160's 2nd channel? Or am I best off to stick with this and do some adapter magic?



Guess I should have done my homework http://www.lsilogic.com/products/obsolete_host_bus_adapters/lsi20860_b.html

[Peter M]

The 20860 is Narrow-Only, and has 50-pin external connector alright. Go count again ;)

[sm8000]

LOL! What a day I'm having... just looked at the thing and figured it was 68-pin, kinda looks like it... Didn't take transfer speed capabilities into account. Thanks Peter, now all I need is a 50-pin external cable, Narrow end to Wide (Centronics) end. I think I can find one without too much trouble, right? :x

[Peter M]

Ye olde Centronics 50-pin plug is still Narrow (8-bit) SCSI. Don't confuse your facts please.

Yes, those cables, modern 50-pin "HD" plug on one end and old Centronics on the other, are quite common. Get a quality cable with proper twisted pair and shielding, else you won't be happy. And make sure the HD plug does have the holding clamps, since these tiny plugs have a tendency of falling off when these clamps are missing.

[sm8000]

Yeah, I screwed up my verbage - I said "Wide" when I should have said "wide" (physically) but I should have said something else ;)

Found a couple of good links to help me figure out what I want - first two hits when I Google for SCSI cables:

http://www.google.com/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=SCSI+cables

Only thing I'm not clear on is - what's the max length I can use?

[Peter M]

That depends on the fastest device on the chain, and on how many devices are on.

If the fastest device on the chain is Ultra-SCSI (20 MB/s), and you have no more than four things on the chain (including the host adapter), then it's three meters total. With more than four devices, the allowable length degrades all the way down to 1.5 meters with eight devices.

At Fast-SCSI (10 MB/s) or slower, you can double those figures.

You can always use the SCSI controller BIOS to put a speed limiter on when the cabling gets too long. I had to do that here on my secondary channel.

Termination should be of the active type on both ends. If the host adapter forms one end, it'll take care of it automatically.

Scanners typically run asynchronous extra-slow SCSI. So don't worry about the cable length, but make sure the scanner has termination on. Some have a switch to enable that, some need a terminator plugged onto their other SCSI connector.

[sm8000]

Nine feet it is :) All I'm planning to have in it (for now) is a DVD-ROM (my USB scanner will do for now). So with this 20860 being adopted as a 2nd channel by the U160, the termination on that end will be taken care of, correct?

As for the other end, I'm using this enclosure (http://www.embeddedlogic.com/TH99/r/M-O/60104.htm) to house said DVD-ROM. I've attached a scan of those two 50-pin Centronics connectors (they are currently removed while it houses my U160 HDD) and an adapter for 50 pins to 68. See how one of the 50-pin Centronics connectors has a plug on it - is that termination? If not, how do I achieve it?

[sm8000]

May have answered my own question - reading this page (http://support.necsam.com/OEM/cd-rom/advmedia/multispin/multispin2x/cdr741/index.htm) tells me that if the drive is hooked up to this enclosure's internal electronics, the termination can be set by a swith on the outside of the enclosure.

Also, FWIW, this page (http://support.necsam.com/OEM/cd-rom/advmedia/multispin/multispin2x/cdr841/index.htm) talks about the CD-ROM that was in this thing (still have it) and it talks about it being jumpered on the drive - I suppose I'd do that if I was using it outside of this enclosure?

[Peter M]

You shouldn't enable termination inside external drive enclosures (besides, U160 drives never have that anyhow). Use the terminator plug you got there.

The narrow-to-wide adaptor must also contain termination, for the "upper" half of the wide bus that ends inside this adapter.

The LSI adapters auto-detect whether one or both of their SCSI connectors are used, and enable/disable their onboard termination accordingly, automagically. No software involved at all.

[sm8000]

You shouldn't enable termination inside external drive enclosures (besides, U160 drives never have that anyhow). Use the terminator plug you got there.

Not doing any termination while the U160 HDD is in there, roger that.

The narrow-to-wide adaptor must also contain termination, for the "upper" half of the wide bus that ends inside this adapter.

That's what I don't understand - not the 'why' of it, but the 'how'. Is that plug I've got sufficient? Do I need to do anything else?

Oh wait ... reading it again I'm realizing you're talking about the 50-to-68 pin adapter, right? I don't know if it has termination ... I can ask the guy who gave it to me. If not, what should I do?

The LSI adapters auto-detect whether one or both of their SCSI connectors are used, and enable/disable their onboard termination accordingly, automagically. No software involved at all.

Works for me, I just let 'em do their thing.

[Peter M]

Just keep your external boxes without termination inside them. That way, you can daisy chain them without headache, plugging an external terminator on the one unused connector on the last device on the far end.

The 50-68 adapter (which is for plugging a Wide device onto a Narrow cable) should have that semi-termination circuitry inside. Else your Wide device won't be happy, because half its SCSI bus is dangling in mid-air.

Note that running a zippy U160 HDD on a U(20) chain is going to stink, performance wise. Better put that into a proper Wide LVD enclosure and hook it onto the U160 adapter.

[sm8000]

I've got it now, thanks. If I get another of these boxes, the plug will go on the one on the end.

I've got the Ultra 160 drive on an Ultra 160 bus - I wish I had a camera to show you what I mean. I have a 68-pin ribbon running from my U160 card's outer port directly to my U160 drive (inside that enclosure), nothing in between.

The ribbon is going through the hole where the above connector was. Looks kinda rag-tag, but works for me :) I'll move the U160 drive into something actually U160 when the time comes.

Thanks again for all your help, it is truly appreciated.