Date: Fri, 30 May 1997 13:50:27 -0600 From: Joshua Fielden <shag@concentric.net> To: Stephen McKay <syssgm@dtir.qld.gov.au> Cc: freebsd-chat@FreeBSD.ORG Subject: Re: IDE or Ultra SCSI Message-ID: <338F2F83.55301D85@concentric.net> References: <199705300343.XAA01738@federation.addy.com> <19970530092929.CP11088@uriah.heep.sax.de> <199705301207.WAA15894@ogre.dtir.qld.gov.au>
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Stephen McKay wrote: > > On Friday, 30th May 1997, J Wunsch wrote: > > >As Francisco Reyes wrote: > > > >> I have been agonizing for a few days trying to decide whether to get > >> IDE or Ultra SCSI. > > > >IDE is in theory as fast as SCSI. However, we don't support busmaster > >DMA for IDE yet, and thus you eat up valuable CPU cycles with an IDE > >drive, that could be spent better in serving processes on a > >multiprocessing system. > > Is IDE (in theory) really as good? I understood that only one outstanding > command was possible with IDE, meaning only one disk could be active at > a time, versus many simultaneous commands with SCSI. Am I out of date? SCSI can still only access two devices at any given time, one initiator <usually, but not always the host adapter> and one target. SCSI II allows for "disconnect" which means a drive can aquire a queue of commands, remove itself from the bus, and reattatch when finished processing those commands, but it obviously is no help for read/write operations. :-) It does speed things up, but not quite to the extent I believe you are thinking of. > > >``Ultra'' is more of a marketing gag than real value, it just means > >``use double the clock rate, and allow for only half the cable > >length''. > > On the other hand, Ultra Wide is where it's all going. Or so it looks to me. > At least until that FireWire stuff is cheap. > > >> The difference in price betwen IDE and Ultra is about $700. Is it worth > >> it? > > > >Why is it so much? > > I ask this often, hoping to have someone tell me it is not so. It is all to > do with volume and margins for middle men. Fewer SCSI disks sold == higher > prices. > > For example, I could go to a nearby computer shop and buy a 6Gb IDE disk > for AU$600, or a 4Gb SCSI3 disk for AU$1100. That's nearly 3 times the > cost per byte. I have no reason to believe that either is better quality > than the other. What a downer. Part of the cost is the controller board. A SCSI drive of Fast Ultra Utlra Wide or SCSI III is faster than an IDE drive, <up to ~3x faster!> and also has the ability to queue commands, spin itself up and down, does its own low-level formatting <according to a fill pattern in the firmware> and has to be able to become "initiator" for bus activity on demand, as well as doing quite a bit more self-diagnostic and error reporting through self-test and sense data. Outside of the sheer fact that the hardware itself is usually a bit better, the card is what drives the price. That and totaly speed. A SCSI-III drive is ~twice the speed of the new 33mb EIDE drives, and SCSI III has been around for a while. > > Or I could buy an 8x SCSI CD-ROM for twice the price of the same model > drive with IDE interface. Sigh. A CD-ROM <until 16x and higher hit> was always so slow that there would be little improvement and I had these IDE busses "rusting" on my board, so I have always gone ATAPI for CD-ROM, but with 16x, I'm not so sure about that. I would say for 8x, don't bother with SCSI if you already have the bus, and you get the added bonus of accessing IDE and SCSI in parallel. i.e: read from the CD and write to the drive simultaneously. > > So I have to keep telling myself what an investment in brain cells I have > with SCSI, how it always works (well it does for me), and how every IDE > system that I've tried to put 2 disks in, or take one drive out of, has > been such a pain that I've given up. Then I calculate my hourly rate into > the equation... > > Even so, I'm not sure if I'll give in this time round and turn to the dark > side. The lure of cheap equipment! :-/ > > Stephen. I have run three mixed IDE/SCSI machines, and used to work for FWB Software, who makes IDE and SCSI device drivers for Mac and Windows, and never have I seen a true benchmark that puts equivalent EIDE drives near enough to SCSI performance to warrant consideration, except for the newer 7200 RPM EIDE that have come out. Of course, I'm also the guy they used to play "guess the drive speed" with at work, because after 1/2 hr-45 minutes I could tell you which was the fastest/slowest drive on a system with differences of only a couple of ms, so I'm a tad biased. :-) JF
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