tak@doe.UToronto.CA (Tak Ariga) (10/10/89)
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?
_____________________________________________________________________________
Tak Ariga | Chief Programmer / System Administrator
..!{utzoo|lsuc}!utdoe!tak | The Dictionary of Old English Project
+1 416 978 8883 | University of Torontordgreenall (10/11/89)
The 600 meg drive I got from Ted Cowie (ted@tvcent) for the 386 system I was on was fantastic. I suggest you drop him an email message and ask him about it since he knows more of the specs than I do. All I can tell you was that this monster drive was fantastic, and installed on SCO XENIX 386 2.3.2 with no problems. richard greenall lethe!chmee!richard
clewis@ecicrl.UUCP (10/12/89)
In article <891011142510.20869@tmsoft.uucp> Tak Ariga <tak@doe.UToronto.CA> 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
woods@eci386.uucp (Greg A. Woods) (10/14/89)
In article <700@ecicrl.UUCP> clewis@ecicrl.UUCP (Chris Lewis) writes: > In article <891011142510.20869@tmsoft.uucp> Tak Ariga <tak@doe.UToronto.CA> 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. > > 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. I'm not sure what the actual limits of the ESDI interface are, but I know the WD1007 controller will only support 2 drives. This give SCSI the advantage when many drives are required. As for performance, it can be shown that using multiple drives in a multi-user system can be a big win, when you have a smart OS (i.e. disk driver) and an interface such as SCSI 2 which will support multiple asyncronous commands. As Chris stated, current drives don't tax either interface in the bandwidth department, though a full complement of 8 fast devices on a SCSI buss might be pushing the limit. > 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. My 3B2 SCSI host adapter has a fast 80186 onboard! The main CPU never waits, unless that's all it has to do. Modern 3B2 systems often use SCSI host adapters and "bridge" controllers such that you can hang 8 bridge controllers, each with 4 large ST506 or ESDI drives, from one host adapter. The 3B2 architecture allows up to 8 host adapters. That's a lot of disk! All in all, I find the SCSI architecture much more elegant.... -- Greg A. Woods woods@{eci386,gate,robohack,ontmoh,tmsoft,gpu.utcs.UToronto.CA,utorgpu.BITNET} +1-416-443-1734 [h] +1-416-595-5425 [w] Toronto, Ontario CANADA
clewis@ecicrl.UUCP (10/14/89)
In article <1989Oct13.194516.3141@eci386.uucp> woods@eci386.UUCP (Greg A. Woods) writes: >In article <700@ecicrl.UUCP> clewis@ecicrl.UUCP (Chris Lewis) writes: >> In article <891011142510.20869@tmsoft.uucp> Tak Ariga <tak@doe.UToronto.CA> writes: >> 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. >I'm not sure what the actual limits of the ESDI interface are, but I >know the WD1007 controller will only support 2 drives. This give SCSI >the advantage when many drives are required. ESDI physically looks like ST506 - same ribbon cables. The SCSI-host ESDI disk DPT controller supports 4 ESDI drives. Don't know if the AT bus one was only two drives or not. I've never seen the ESDI interface spec either, so I couldn't tell you the number of LUN's you can theoretically connect. >As for performance, it can be shown that using multiple drives in a >multi-user system can be a big win, when you have a smart OS (i.e. disk Which is why I said two drives (or more) for better performance than a single drive. >driver) and an interface such as SCSI 2 which will support multiple >asyncronous commands. ESDI obviously does because each of the drives has it's own cables. You also have to remember that these commands (in SCSI) aren't fully asynch... >As Chris stated, current drives don't tax >either interface in the bandwidth department, though a full complement >of 8 fast devices on a SCSI buss might be pushing the limit. Um, well, I didn't mean to imply that. 2 SCSI drives running at a hundred or two K bytes per second each will probably come close to saturating even SCSI 2. Queueing theory and all that. Which is why the preferred Spectrix configuration was a host adapter and controller *per* drive (well, the earlier controllers didn't support disconnect, but the later ones did allow overlapping seeks). >> 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. > >My 3B2 SCSI host adapter has a fast 80186 onboard! Good for you. Too bad your disks don't work ;-( >The main CPU never >waits, unless that's all it has to do. Modern 3B2 systems often use >SCSI host adapters and "bridge" controllers such that you can hang 8 >bridge controllers, each with 4 large ST506 or ESDI drives, from one >host adapter. The 3B2 architecture allows up to 8 host adapters. >That's a lot of disk! >All in all, I find the SCSI architecture much more elegant.... SCSI is very elegant for relatively inexpensive solutions. But not blazingly fast.... I've worked on SCSI stuff for a long time. And had, until about a year ago said "heck, the only difference between ESDI and SCSI is that the transfer rate's faster. Why bother?" None of the machines I was working on cared. And ESDI driver's are pretty complicated. Funny thing, *nobody* we talked to was interested in SCSI. When I was working on the DPT drivers, I had a lot of contact with the DPT engineering staff (trying to find a host adapter that worked...). The DPT's I was working with were SCSI interface to the host, and ESDI to the disks. I asked him whether they'd ever support SCSI drives. The response was "are you nuts?". I know, get both worlds: buy the DPT SCSI-host version of the board, and use SCSI drivers for your ESDI disks.... (which is the same as the configuration I worked on and the 3b2's). -- 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