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Xref: sserve comp.arch:27931 comp.unix.bsd:7550 comp.os.linux:14998 Newsgroups: comp.arch,comp.unix.bsd,comp.os.linux Path: sserve!manuel.anu.edu.au!munnari.oz.au!sgiblab!zaphod.mps.ohio-state.edu!cs.utexas.edu!uunet!walter!gizmo!mo From: mo@gizmo.bellcore.com (Michael O'Dell) Subject: Re: IDE faster than Mips SCSI disk????? Message-ID: <1992Nov6.142946.17430@walter.bellcore.com> Keywords: Sender: news@walter.bellcore.com Nntp-Posting-Host: gizmo.bellcore.com Reply-To: mo@bellcore.com Organization: Center for Chaotic Repeatabilty References: <1992Nov6.033942.21194@ntuix.ntu.ac.sg> Date: Fri, 6 Nov 92 14:29:46 GMT Lines: 27 from our experiences trying to qualify drives and controllers for a computer project i was involved with a few years ago.... one must be very careful that one isn't comparing the performance of two disk controllers and not the attached drives. it is VERY tricky to sort out why one disk goes faster than another, and when and under what circumstances. controller startup latencies vary by geologic timescales, or so it seems if one tries hard to measure them accurately. we'll not even go into latencies caused by the number of times the controller must be touched to actually start a transfer. the same caveats apply to measuring the performance of the underlying drive and electronics (with it's embedded controller <see above>) versus measuring the performance of the transfer channel implementation. transfer channel protocols (IDE vs SCSI-2) are compared with timing diagrams, but that is admittedly less interesting than comparing implementations which govern what one really gets. the problem, however, is really *knowing* what one is measuring. -Mike O'Dell Bellcore??? Bellcore isn't allowed opinions. Any found here are mine.