Date: Thu, 7 Aug 1997 22:08:44 -0600 (MDT) From: Atipa <freebsd@atipa.com> To: dyson@FreeBSD.ORG Cc: George Michaelson <ggm@connect.com.au>, current@FreeBSD.ORG Subject: IDE vs SCSI was: flags 80ff works (like anybody doubted it) Message-ID: <Pine.BSF.3.91.970807215005.4224A-100000@dot.ishiboo.com> In-Reply-To: <199708080239.VAA01532@dyson.iquest.net>
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On Thu, 7 Aug 1997, John S. Dyson wrote: > > > > > > > > looks like 20%+ speedup across the board. Definately worth it. > > > > > > next stop, DMA. > > > > Not to be rude, but you'd probably get an equall great increase if not > > more so by switching to SCSI, along with reduced cpu usage. > > > > Sure. but I don't have the $$$ to do this. Anyway, if there is milage > > in making ISA work, I might as well try it. > > > Well, I have both SCSI and IDE. If I just need another 4GB or so, I can > just slap in a $250 IDE drive and be done with it. Hope to have a Promise > controller driver running soon, and that will allow a total of 8 of the > little IDE jellybeans (some people have other names for them, but those > names aren't very polite) in my machine. :-). The main advantage with SCSI is the speed of the drive; not the interface. Typically SCSI drives are 5400RPM at worst, and IDEs are 5400RPM at best. I do not see IDE drives getting those 7-8ms seek times either. Good seeks for IDE are 10ms, roughly 30% slower than SCSI. Doing a very crude benchmark: $ time dd if=/dev/zero of=/tmp/file1 bs=1024 count=20000 $ time dd if=/tmp/file1 of=/dev/null bs=1024 count=20000 $ time dd if=/tmp/file1 of=/tmp/file2 bs=1024 count=20000 "Identical" (Quantum Fireball ST 6.4GB IDE/SCSI) drives have almost identical results. SCSI will be better with multiple drives, but in this case not worth the expense IMHO, especially when the cost of the host adapter is included. If you need really good performace (NFS server, news, etc.), SCSI is far superior. Using the above "benchmark", our Atlas-II drives go about 17MB/sec on files up to 40MB. On arbitrarily large files (200MB plus), the sustained throughput is about half that. Due to the lower rotational speed, IDE drives are actually more reliable in my experience. You'd be surprised how long an engine lasts when it never exceeds 55 miles per hour! I would not recommend a Cheetah for any mission critical machine. It produces so much heat that the system in general is jeopardized. Looking at all the last second "wire jumpers" on the PCB does not make me any more comfortable with the design. I'd wait for the next wave of 10,000RPM drives to hit the market. Kevin
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