Date: Tue, 01 Apr 2003 09:23:26 -0500 From: Jason Andresen <jandrese@mitre.org> To: "Greg 'groggy' Lehey" <grog@freebsd.org> Cc: FreeBSD Stable List <freebsd-stable@freebsd.org> Subject: Re: vinum performance Message-ID: <3E89A0DE.7040505@mitre.org> In-Reply-To: <20030401004953.GE34617@wantadilla.lemis.com> References: <20030330125138.K23911@leelou.in.tern> <3E870CC7.5000204@mac.com> <20030330175605.E23911@leelou.in.tern> <3E87204C.5060304@ludd.luth.se> <3E88524A.1060600@mitre.org> <3E88AECD.10607@liwing.de> <3E88B601.90802@mitre.org> <20030401004953.GE34617@wantadilla.lemis.com>
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Greg 'groggy' Lehey wrote: >>>>I get 4565 K/sec on modern ATA/133 HDDs. >>>> >>>>Reading is much better at 91908 K/sec at least. >> >>Well, I'm writing 200MB files most of the time, so the stripe size is >>not an issue. I'm just wondering why the reads are *20* times faster >>than the writes. > > > They're not. I don't know where you get that read figure from, but no > disk can transfer that fast, and you don't appear to be doing multiple > transfers in parallel. That was what bonnie++ reported. >>I think the read performance was CPU limited in this case. > > > I think you were reading from cache. Quite possible. I'm not sure how bonnie handles that. >>While some of this is probably an oddity with bonnie (Bonnie always >>reports my writes to be about half as fast as the reads, but dd >>thinks otherwise: >> >>(Both of these were on previously untouched files to prevent any >>caching, and the "write" test is on a new file, not rewriting an old one) >>Write speed: >>81920000 bytes transferred in 3.761307 secs (21779663 bytes/sec) >>Read speed: >>81920000 bytes transferred in 3.488978 secs (23479655 bytes/sec) >> >>But on the RAID5: >>Write speed: >>81920000 bytes transferred in 17.651300 secs (4641018 bytes/sec) >>Read speed: >>81920000 bytes transferred in 4.304083 secs (19033090 bytes/sec) > > > Yes, this is very close to the 4:1 ratio that I would expect. If > you're looking for write performance, don't use RAID-5. So FreeBSD never optimizes out those first two operations? I was thinking writing fresh large files to a RAID5 array would only be half as fast as reading. -- \ |_ _|__ __|_ \ __| Jason Andresen jandrese@mitre.org |\/ | | | / _| Network and Distributed Systems Engineer _| _|___| _| _|_\___| Office: 703-883-7755
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