Date: Mon, 22 Jan 2001 21:10:37 -0700 From: "Kenneth D. Merry" <ken@kdm.org> To: Ian Cartwright <icartwright@mediaone.net> Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: SCSI Speed Question Message-ID: <20010122211037.A84856@panzer.kdm.org> In-Reply-To: <01012222480104.00373@ian.batcave.com>; from icartwright@mediaone.net on Mon, Jan 22, 2001 at 10:48:01PM -0500 References: <01012222480104.00373@ian.batcave.com>
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On Mon, Jan 22, 2001 at 22:48:01 -0500, Ian Cartwright wrote: > I have a question about the speed of my SCSI devices, especially under > FreeBSD. I currently have an Adaptec 2940U/w Fast/Wide controller with two > Compaq Fast/Wide hard disks, and Toshiba SCSI II cdrom and an HP SCSI II DAT > Drive. My question is, is this the optimum configuration to support the > highest transfer rate for my hard disks? Does the SCSI bus run at the speed > of the slowest device on the bus or can I run it in asynchronous mode? If I > can run in async mode, how do I tell FreeBSD to do it? Yes, you are running at the fastest speeds possible for your hardware. In your case, no, the SCSI bus doesn't run at the speed of the slowest device on the bus. (*) If you run in async mode, that will slow things down significantly. I think you can make your devices negotiate async like this: camcontrol negotiate da0 -v -R 0 -a (*) With LVD busses (i.e. this doesn't apply in your case), the entire LVD bus segment will be restricted to single-ended speeds (20MHz maximum) if there is one device on that bus segment that can't do LVD. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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