Date: Wed, 12 Dec 2001 16:23:09 +1030 From: Greg Lehey <grog@FreeBSD.org> To: Wilko Bulte <wkb@freebie.xs4all.nl> Cc: Matthew Dillon <dillon@apollo.backplane.com>, Mike Smith <msmith@FreeBSD.org>, Terry Lambert <tlambert2@mindspring.com>, Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de>, freebsd-current@FreeBSD.org Subject: Re: RAID performance (was: cvs commit: src/sys/kern subr_diskmbr.c) Message-ID: <20011212162309.J82733@monorchid.lemis.com> In-Reply-To: <20011211234151.A72046@freebie.xs4all.nl> References: <200112101754.fBAHsRV01202@mass.dis.org> <200112101813.fBAIDKo47460@apollo.backplane.com> <20011210192251.A65380@freebie.xs4all.nl> <200112101830.fBAIU4w47648@apollo.backplane.com> <20011211110633.M63585@monorchid.lemis.com> <20011211153437.A69755@freebie.xs4all.nl> <20011212090034.C67986@monorchid.lemis.com> <20011211234151.A72046@freebie.xs4all.nl>
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On Tuesday, 11 December 2001 at 23:41:51 +0100, Wilko Bulte wrote: > On Wed, Dec 12, 2001 at 09:00:34AM +1030, Greg Lehey wrote: >> On Tuesday, 11 December 2001 at 15:34:37 +0100, Wilko Bulte wrote: >>> On Tue, Dec 11, 2001 at 11:06:33AM +1030, Greg Lehey wrote: >>>> On Monday, 10 December 2001 at 10:30:04 -0800, Matthew Dillon wrote: >>>>> > > .. > >>>>> and will go down the drain for reads if you cross a stripe - >>>>> something that is quite common I think. >>>> >>>> I think this is what Mike was referring to when talking about parity >>>> calculation. In any case, going across a stripe boundary is not a >>>> good idea, though of course it can't be avoided. That's one of the >>>> arguments for large stripes. >>> >>> In a former life I was involved with a HB striping product for SysVr2 >>> that had a slightly modified filesystem that 'knew' when it was >>> working on a striped disk. And as it know, it avoided posting I/O s >>> that crossed stripes. >> >> So what did it do with user requests which crossed stripes? > > Memory is dim, but I think the fs code created a second i/o to the > driver layer. So the fs never sent out an i/o that the driver layer had > to break up. That's what Vinum does. > In case of a pre-fetch while reading I think the f/s would just > pre-fetch until the stripe border and not bother sending out a > second i/o down. Yes, that's reasonable. > In the end all of this benchmarked quite favorably. Note that this > was 386/486 era, with the classic SysV filesystem. I don't think that UFS would behave that differently, just faster :-) Greg -- See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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