Date: Mon, 8 May 1995 12:29:49 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: tom@haven.uniserve.com (Tom Samplonius) Cc: hackers@FreeBSD.org Subject: Re: Is a 486 fast enough for SCSI? Message-ID: <199505081929.MAA01292@gndrsh.aac.dev.com> In-Reply-To: <Pine.BSF.3.91.950508121705.2024B-100000@haven.uniserve.com> from "Tom Samplonius" at May 8, 95 12:26:33 pm
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> > > I've got a AMD486DX4100 with an Adaptec 2940 and two SCSI drives. When > I run iozone on one drive I get about 1.9MB/s, but when I run a iozone on > each drive I get about .9 MB/s (roughly half). Since the SCSI bus runs > at 10MB/s per second, the limiting factor appears to be the CPU? I > thought PCI devices required very little CPU time? It is not the CPU, but you failed to mention which version of FreeBSD and particularly the ahc driver you are running. I suspect that the driver may be detuned for compatibility reasons, but Justin is the one who would know best on that. You also failed to mention the model of the drives, a parameters like RPM that greatly effect the raw data rate of the drive (if you have the media transfer rate number that is the best one to use, it is usually a range of values due to ZBR recording. The higher number is what you get for the outer cyclinders, the lower number for the inner cylinders). I can easily do 4MB/sec using a DX33 EISA system with an AHB1742 controller and DEC 3053L disk drives (Media transfer rate is 2.5-5.5MB/sec). This is with FreeBSD 1.x through to FreeBSD 2.x-current, but only because the ahb driver has been stable pretty much the whole time. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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