Date: Mon, 25 Oct 2004 18:08:24 -0400 From: Charles Swiger <cswiger@mac.com> To: Brad Knowles <brad@stop.mail-abuse.org> Cc: Scott Long <scottl@freebsd.org> Subject: Re: FreeBSD 5.3b7and poor ata performance Message-ID: <64029B30-26D2-11D9-9A2F-003065ABFD92@mac.com> In-Reply-To: <p06002061bda3224cd029@[10.0.1.3]> References: <14479.1098695558@critter.freebsd.dk> <417D25E8.6080804@ng.fadesa.es> <200410251928.01536.victor@alf.dyndns.ws> <"200410251837.58257.Thoma s.Sparrev ohn"@btinternet.com> <417D3F12.20302@DeepCore.dk> <417D40A1.9030802@ng.fadesa.es> <417D45F1.9090504@freebsd.org> <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com> <F5F15CA0-26C5-11D9-9A2F-003065ABFD92@mac.com> <417D65F1.2040809@freebsd.org> <p0600205fbda318006656@[10.0.1.3]> <417D6F4C.9000404@freebsd.org> <p06002061bda3224cd029@[10.0.1.3]>
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On Oct 25, 2004, at 5:39 PM, Brad Knowles wrote: > At 3:25 PM -0600 2004-10-25, Scott Long wrote: >> But as was said, there is always >> a performance vs. reliability tradeoff. > > Well, more like "Pick two: performance, reliability, price" ;) That sounds familiar. :-) If you prefer... ...consider using: ---------------------------------------------- performance, reliability: RAID-1 mirroring performance, cost: RAID-0 striping reliability, performance: RAID-1 mirroring (+ hot spare, if possible) reliability, cost: RAID-5 (+ hot spare) cost, reliability: RAID-5 cost, performance: RAID-0 striping >> And when you are talking about RAID-10 with a bunch of disks, you >> will indeed start seeing bottlenecks in the bus. > > When you're talking about using a lot of disks, that's going to be > true for any disk subsystem that you're trying to get a lot of > performance out of. That depends on your hardware, of course. :-) There's a Sun E450 with ten disks over 5 SCSI channels in the room next door: one UW channel native on the MB, and two U160 channels apiece from two dual-channel cards which come with each 8-drive-bay extender kit. It's running Solaris and DiskSuite (ODS) now, but it would be interesting to put FreeBSD on it and see how that does, if I ever get the chance. > The old rule was that if you had more than four disks per channel, > you were probably hitting saturation. I don't know if that specific > rule-of-thumb is still valid, but I'd be surprised if disk controller > performance hasn't roughly kept up with disk performance over time. That rule dates back to the early days of SCSI-2, where you could fit about four drives worth of aggregate throughput over a 40Mbs ultra-wide bus. The idea behind it is still sound, although the numbers of drives you can fit obviously changes whether you talk about ATA-100 or SATA-150. -- -Chuck
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