Date: Fri, 26 Oct 2001 17:59:29 -0700 (PDT) From: Matthew Jacob <mjacob@feral.com> To: Greg Lehey <grog@FreeBSD.org> Cc: Doug Rabson <dfr@nlsystems.com>, Luigi Rizzo <rizzo@aciri.org>, John Baldwin <jhb@FreeBSD.org>, Jonathan Lemon <jlemon@FreeBSD.org>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: RAID-5 parity calculations (was: cvs commit: src/sys/dev/fxp if_fx) Message-ID: <Pine.BSF.4.21.0110261757260.12956-100000@beppo> In-Reply-To: <Pine.BSF.4.21.0110261753401.12956-100000@beppo>
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I guess the real question is: 'can you get the parity calculations done in time so that the entire stripe can go out together'. This obviously doesn't really work for the first request unless you delay it. If you have a hugely deep queue, you will burn your central processor doing things that are not germane to regular systems work- you can't help but be assisted by a coprocessor doing that work (it's like bcopy h/w). On Fri, 26 Oct 2001, Matthew Jacob wrote: > > Sorry, that seems wrong to me. Typical RAID write performance for something > like an Sun A1000 which has a pentium in it is about 50% of theoretical. > > > On Sat, 27 Oct 2001, Greg Lehey wrote: > > > On Thursday, 25 October 2001 at 15:24:06 -0700, Matt Jacob wrote: > > > > > > And the fastest software RAID-V I've known was at NASA/Ames on the > > > Convex 3280s- they used the otherwise unused vector units for parity > > > calculations- this gave write performance for a 22 wide stripe on a > > > terabyte fileystem to be at about 88% of theoretical maximum, which > > > sure aint' bad. > > > > The parity calculations for RAID-5 are several orders of magnitude > > faster than the disk accesses. Even on a 486, they took hardly any > > time. > > > > Greg > > -- > > See complete headers for address and phone numbers > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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