Path: utzoo!mnetor!motto!ecijmm!ecicrl!clewis From: clewis@ecicrl.UUCP Newsgroups: can.usrgroup Subject: Re: Hard Drives: SCSI or ESDI Message-ID: <700@ecicrl.UUCP> Date: 12 Oct 89 04:54:05 GMT References: <891011142510.20869@tmsoft.uucp> Reply-To: clewis@ecicrl.UUCP (Chris Lewis) Distribution: ont Organization: Elegant Communications Inc., Ferret Division, Toronto, Canada Lines: 55 In article <891011142510.20869@tmsoft.uucp> Tak Ariga writes: >With all this talk about hard drive interleave and capacity, I was wondering >whether I should go ESDI or SCSI for our next big hard drive for our Xenix >system. >It would be in 300MB range, probably a Micropolis, but considering cost/ >performance/future trends/etc. is SCSI better than ESDI, or vice versa? SCSI has a few advantages over ESDI. For example, SCSI is a peripheral bus, but ESDI is a *disk* bus. Hence, you can't hang your tape drive, or zuper-whizzbang video interface on a ESDI interface, but you can on a SCSI. Then again, bus contention usually makes the performance pretty lousy. SCSI drives usually cost a teensy bit more than their ESDI counterparts. SCSI is a slightly more complicated interface and needs somewhat more intelligence. Current *official* SCSI specifications place SCSI transfer rate at about 1/3 - 1/2 that of ESDI (1Mb - 1.5Mb vs 2Mb/sec). There exist some SCSI implementations that have the same transfer rates as ESDI. However, remember that these are instantaneous bandwidth figures, and you will *never* see performance like this in real life. And secondly, you can only get the bits of the disk at the rotational speed of the drive. MFM is approx 522K/sec, RLL 1.5 times that, SCSI and ESDI double, SMD normally triple, 7200 RPM anybody?. And, this is with 1:1 interleave. For price-no-object blow-out performance, go with *two* ESDI drives and DPT disk caching controllers and *lots* of cache. Believe me, given a reasonable high-horse 386 motherboard, the DPT will turn it into a screamer. I have personally measured thruputs of 1.1Mb/sec *real* I/O and >3Mb/sec cache hit with the DPT on a Maxtor 760 MB ESDI drive. For middle of the road, both SCSI and ESDI will cost and perform about the same, tho the edge is likely to be somewhat towards ESDI, especially with multiple drives. Eg: A Western Digital WD1007. Highly recommended. The really nice thing about the DPT and the WD1007 is that they're AT-transparent, and you don't need extra drivers. Do NOT under any circumstances use a dumb SCSI or ESDI board that doesn't have it's own DMA facilities. AT DMA is ~300Kb/sec. - eg, *very slow*. Further, don't use controllers that do programmed I/O. Yes, a 386 can transfer pretty bloody fast, but with this sort of controller you may miss other interrupts, and you don't get to use the processor for real work during I/O operations. -- Chris Lewis, Elegant Communications Inc. UUCP: {uunet!mnetor, utcsri!utzoo, uunet!attcan!lsuc, yunexus}!ecicrl!clewis Moderator of the Ferret Mailing List (ferret-request@eci386) Phone: (416)-294-9253