pfh@craycos.com (Peter Hill) (09/21/90)
I received nine replies to my request for information about SCSI extenders. There appear to be fiber-optic extenders, but none of my correspondents had any experience with them. One solution that several people recommended is a pair of single-ended/differential conversion boards. Just about everybody mentioned Rancho Technology at (714) 987-3966 as a source for these boards. See below for other sources. Below are the replies. Thanks, guys. ___________________________________________________________________________ >From: stevem@CFSMO.Honeywell.COM (Steve Mestad) i faced that problem about 2 yrs ago. the solution i used was found to be a pair of scsi single ended to differential ended converter boards. you can go 6m on each single end and i think 25 m on the differential run. it has no speed penalty. the converter boards were purchased from rancho technology for about $125 each. they are designed for being built into equipment so its really bare bones. you will need a cabinet, power supply, switches, etc to make it into a stand alone box if you are planning to use them as a generic extender. [Rancho now offers a stand-alone version.--PFH] we extended 1 bus that way and used it for a while and our need ended as we switched tactics and didn't need to extend the bus anymore. the idea worked quite well, we extended the bus about 20 meters, saw no performance degradation (although i doubt we were pushing the 4 meg/sec limit) and all performed as expected. the only thing we did see was that powering on and off the extenders could put a glitch on the bus so power up sequence was to fire up the extenders and then the peripherals. i have seen scsi extenders as off the shelf products from places such as black box that could go as far as 1000 ft but all of them i have seen had severe performance degradation. hope this info helps. it took me about 2 days of phone calling to come up with the rancho board when i needed it. ___________________________________________________________________________ >From: jiro%trumpet.CIT.CORNELL.EDU@CORNELLC.cit.cornell.edu (Jiro Nakamura NeXT Developer) I have the feeling that 50 feet is way, way beyond the allowed limit for single-ended SCSI buses. I had the feeling that 12ft was the minimum. I could check the SCSI manual if you wanted, but 50 ft is definitely unkosher. If you tried using a double-ended you may get a bit further, but SCSI is a high-speed bus (hah!), signal propagation delays along a 50ft cable would be just too long (IMHO). ___________________________________________________________________________ >From: Mike Rembis <mrembis%xphoton.com@ICS.UCI.EDU> There is a device that utilizes a fiber-optic link between two decoders allowing for a VERY long SCSI bus. If I can find the leaflet, I will forward you the company's bio. ___________________________________________________________________________ >From: jak@apollo.com (Jack Murphy, Apollo/HP) I'd suggest getting two Rancho Technology single-ended/differential adapter boards; convert to differential as you leave the cpu box and switch back to single-ended when you get to the disk. We've played with a couple in the lab and were running a 4mbyte/sec synchronous drive at 100' with no problems. I've also read a fairly thorough test report that `proved' the boards would work just fine (there was one possible timing problem that I don't remember but it didn't seem significant). ___________________________________________________________________________ >From: @polari@sumax.seattleu.edu (MDL Corporation, Bellevue, WA (206) 643-7333) A company that had a booth at Comdex last November was offering such a beast, but it was rather expensive at (then) $475 each for a box at each end of a coax cable, for a total cost of $950. They also offered the same thing using fiber optics for $1640. They claim to extend the bus up to 1,000 feet. I know nothing else about them except for their data sheet, which says their SC20 and SF40 Extenders work with devices "that conform to the full SCSI ANSC XT9.2 standard". (sic) ___________________________________________________________________________ >From: cgn@leo.UUCP (Chris Nieves, ICL North America, Irvine, CA) Rancho Technology in CA has a single-end to differential converter. If you buy two, connecting the differential side of each board with your fifty foot cable, it just might work. Their number is (714) 987-3966. We've used this product to extend a single-end bus but did not do a lot of testing to see how reliable it was. We've also use this product to attach a single-end tape to a differential host. ___________________________________________________________________________ >From: jlohmeye%entec.wichita.ncr.com@RELAY.CS.NET (John Lohmeyer, NCR Corp., Wichita, KS 67226, 316-636-8703) Yes, there are a few around. I built an engineering prototype several years ago (circa 1986), but my employer decided to not develop it into a product. Since then I have heard of several companies in various stages of development: HP Contact Kurt Chan: kc@hprnd.hp.com Methode Contact Bob Masterson: Voice: (303) 695-1333 There are others that I can't think of off the top of my head. These devices use fiber optics (or coax) and all have performance impacts. If you only need to go 50-100 feet, consider using differential devices. A single-ended/differential convertor may help, but be aware that ALL such devices introduce signal delays which can reduce the total usable cable length. Two possible sources for translator devices are Rancho Technology (714) 987-3966 and NCR (800) 325-SCSI. (I think the NCR design is superior, but you may consider me biased.) ___________________________________________________________________________ >From: "T.Sippel-Dau/240000" <cmaae30%cc.ic.ac.uk@pucc.PRINCETON.EDU> (Thomas Sippel - Dau, Imperial College Computer Center, UK) You may have some difficulty there, since the response times are quite closely defined. You can try to get two single ended <==> differential converter boxes, and a length of 50 way twist'n'flat scsi cable, or alternatively, take two Sun 3/50 or Sun 3/60 that nobody wants any more and run a bit of ethernet cable between them. ___________________________________________________________________________ >From: blair@pyro.ei.dupont.com (Grant C Blair, DuPont Imaging Systems, Newark, DE 19702, USA) We use the Rancho Technology differential SCSI adaptor for our applications that require a long SCSI connection. It's a really cheap little board that fits in the palm of your hand and goes into the SCSI chain at either end of the really long (more than 30 feet) stretch. 50 feet is no problem using the Rancho adaptors - we regularly use in excess of 100 feet. ___________________________________________________________________________ [end of summary] -- ___________________________________________________________________________ Peter Hill pfh@craycos.com +1 719 540 4259 Cray Computer Corporation, 1110 Bayfield Drive, Colorado Springs, CO 80906
jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer) (09/24/90)
Since I responded to this posting, I have been contacted by another possible source of SCSI extenders. Applied Concepts (619-453-0090) makes both a SCSI repeater ($375 quantity 1) and a fiber optic SCSI extender ($975 quantity 1 -- you need two). I have not tried these devices and have no information about the company other than the phone number, above. -- John Lohmeyer John.Lohmeyer@Wichita.NCR.COM NCR Corp. uunet!ncrlnk!ncrwic!entec!jlohmeye 3718 N. Rock Rd. Voice: 316-636-8703 Wichita, KS 67226 SCSI BBS 316-636-8700 300/1200/2400 24 hours -- John Lohmeyer John.Lohmeyer@Wichita.NCR.COM NCR Corp. uunet!ncrlnk!ncrwic!entec!jlohmeye 3718 N. Rock Rd. Voice: 316-636-8703 Wichita, KS 67226 SCSI BBS 316-636-8700 300/1200/2400 24 hours