Article 13531 of comp.arch.storage: Newsgroups: comp.periphs.scsi,comp.arch.storage,comp.publish.cdrom.hardware Path: charnel.ecst.csuchico.edu!xmission!eli!dsw-eurorscg!nebo.vii.com!uunet!in3.uu.net!204.127.130.5!worldnet.att.net!ix.netcom.com!fadden From: fadden@netcom.com (Andy McFadden) Subject: SCSI termination and related items Message-ID: Organization: Lipless Rattling Crankbait References: <32dd2497.12624361@news.wustl.edu> <32e26963.6378223@news.aimnet.com> <01bc0680$7a9e3360$b6a2dece@richard> <32e3c4e5.26271119@news.aimnet.com> Date: Mon, 20 Jan 1997 23:06:05 GMT Lines: 133 Sender: fadden@netcom4.netcom.com Xref: charnel.ecst.csuchico.edu comp.periphs.scsi:79366 comp.arch.storage:13531 comp.publish.cdrom.hardware:25719 In article <32e3c4e5.26271119@news.aimnet.com>, John Navas wrote: >[POSTED TO comp.periphs.scsi] >>If I would have a termination problem, how come the Advansys card works >>just fine with the same configuration? The only thing I did to correct the >>problem I had is to remove the old Adaptec 2940 from the slot and replace >>it with Advansys 960.... > >For example, you might have had termination set on one card and not the >other. Here's something Bertel Schmitt sent me several months ago regarding SCSI cables and termination. He's the sysop for Adobe Premiere on Compuserve (GO ADOBEAPP), and the author of a very nice article on A/V hard drives (see ftp://ftp.netcom.com/pub/fa/fadden/avdrive.txt). Thought this might be of general interest. Granite Digital can be found on the web at http://www.scsipro.com/. ----- Date: Fri, 31 May 1996 22:59:01 -0400 To: fadden@netcom.com (Andy McFadden) From: Bertel Schmitt [ reformatted for 80 columns ] Terminate your drive - with extreme prejudice. By Bertel Schmitt When attempting to wring every last bit of speed out of your SCSI drives, watch your SCSI cables and watch your termination - with extreme prejudice. Bad (i.e. cheap) cables, long cable runs and passive termination (or - gasp - none at all) of your SCSI drives is an invitation to disaster. If the setup fails outright, then you are actually in luck, because it makes you do something about it. What's more insidious is a marginal setup. The drives work, but they work slower: as signal quality goes down, retries pile up. Your frames drop. Here is my strategy: 1.) Avoid external cables as much as possible. If you need external cables, use only high quality ones (expect to pay a hefty price for them), and try to keep them down to a bare minimum. 2.) Flat cables are much better than round cables. In a flat cable, every other wire is a ground wire which provides perfect shielding. If you absolutely have to connect a stack of external devices, consider flat cable for connection of the stack. Run a high quality round cable to the first device in the stack and then daisy-chain the remaining stack of devices with flat cable. For narrow devices (which are the bulk of externals) you need 50-strand flat cable with crimped-on Centronics-50 connectors (male). If you have a modicum of manual dexterity, you can make them yourself with a vise, or you can order them from a place that makes them. More on that below. 3.) Use ACTIVE TERMINATORS at both ends of the chain. If you are just running a CD-ROM off a SB16 SCSI, you can get away with passive plugs, if you are running a hot drive on a hot controller, use ACTIVE TERMINATORS. If you use SCSI-2, use ACTIVE TERMINATORS. If you run wide or Ultra SCSI, you MUST use ACTIVE TERMINATORS. Many drives have internal terminators which can be activated with a jumper, some of these are passive. Also, the on-drive active terminators are usually not top-of-the line. My recommendation: forget them, and always use a standalone active terminator at both ends of the chain. 4.) In my opinion, the best active terminators are made by Granite Digital (510-471-6267). They've started this years ago with their SCSIVue terminator. Looked a bit cheesy with its golden paint, but it worked. Worked wonders sometimes. Solved many SCSI problems for me and actually "healed" a marginal cable (not to be recommended, but in a pinch...). Recently, they've gone to black, which looks pretty slick. These terminators are available in narrow and wide and are worth their weight in...black. 5.) Granite also makes extremely high quality external cables (glossy black marvels). 6.) While making your own 50-starnd flat cable is fairly easy, crimping 68pin wide cables can be a pain. The wires are much thinner and the job has to be done with extreme precision. After wasting $200 for cables and connectors (if just one connector on the cable is crimped the wrong way, the whole cable can stop working...), I started ordering them from places that do that for a living. Granite also makes custom flat cables with silver wire and teflon coating. (Always order them with 2 extra connectors ... you will be adding drives.) 7.) Wide-to-narrow. This can be a nasty situation. You have a wide controller, but you have to attach a narrow device (like a CD-ROM player) to it. If you have an Adaptec 2940 controller and the device is internal: no problem. The 2940 has an extra narrow connector inside. The manual recommends against using the internal & external wide plus the internal narrow connectors together, but if you keep the length of the internal narrow cable short (and if your use ACTIVE TERMINATION) you shouldn't have a problem. 8.) What if the narrow devices are external? Well, you can buy a cable that plugs into the wide connector at the back of the controller and the other end of the cable plugs into a standard Centronics-50 socket. WATCH OUT! Too often, these cables leave the remaining data lines of the wide connection open (wide has 16 data lines, narrow has 8). Result: termination problems. What to do: you can either run a flat cable from the internal narrow connector to a bracket and then proceed as usual with a narrow connection. Or you buy an external adapter cable, that actively terminates the remaining wide lines. Granite has those too. 9.) If you have a 3940 dual channel wide controller, and you need to connect narrow devices, then you are in a bind. No place for a narrow connector. Granite offers an electronic assembly that crimps on a wide flat cable (let them do it) and that does the adapting electronically as above. 10.) While talking to Granite's tech, he pointed out that even the best narrow-to-wide adapter with active termination will slow fast drives down. The reason: 8 wires will be double-terminated. So despite losing a sale, he recommended to get an extra controller if you have a 3940 and need to run narrow devices. Infamous last words: this may sound like the talk of audio-nuts who run heavy-duty monster cables from their amps to their speakers (and who actually claim that they can hear the difference). Believe me, it ain't so. I use el cheapo lamp cord to connect my speakers (my wife says I'm hard of hearing anyway...) but for my SCSI drives: use those heavy duty cables. And don't forget: always use... right you are. -- fadden@netcom.com (Andy McFadden) [These are strictly my opinions.] PGP Fight Internet Spam - http://www.vix.com/spam/