Date: Wed, 26 Sep 2007 12:17:56 -0500 From: "Rick C. Petty" <rick-freebsd@kiwi-computer.com> To: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-fs@FreeBSD.org Subject: Re: Writing contigiously to UFS2? Message-ID: <20070926171756.GB41567@keira.kiwi-computer.com> In-Reply-To: <20070926175943.H58990@delplex.bde.org> References: <46F3A64C.4090507@fluffles.net> <46F3B4B0.40606@freebsd.org> <fd0em7$8hn$1@sea.gmane.org> <20070921131919.GA46759@in-addr.com> <fd0gk8$f0d$2@sea.gmane.org> <20070921133127.GB46759@in-addr.com> <20070922022524.X43853@delplex.bde.org> <20070926031219.GB34186@keira.kiwi-computer.com> <20070926175943.H58990@delplex.bde.org>
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On Wed, Sep 26, 2007 at 06:37:18PM +1000, Bruce Evans wrote: > On Tue, 25 Sep 2007, Rick C. Petty wrote: > > >On Sat, Sep 22, 2007 at 04:10:19AM +1000, Bruce Evans wrote: > >> > >>of disk can be mapped. I get 180MB in practice, with an inode bitmap > >>size of only 3K, so there is not much to be gained by tuning -i but > > > >I disagree. There is much to be gained by tuning -i: 224.50 MB per CG vs. > >183.77 MB.. that's a 22% difference. > > That's a 22% reduction in seeks where the cost of seeking every 187MB > is a few mS every second. Say the disk speed 61MB/S and the seek cost > is 15 mS. Then we waste 15 mS every 3 seconds with 183 MB cg's, or 2%. > After saving 22%, we waste only 1.8%. I'm not sure why this discussion has moved into speed/performance comparisons. I'm saying 22% difference in CG size. > Since I > got to within 1% of the raw disk speed, there is little more to be > gained in speed here. (The OP's problem was not speed.) I agree-- why are you discussing speed? I mean, it's interesting. But I was only discussing CG sizes and suggesting using the inode density option to reduce the amount of space "wasted" with filesystem metadata. I do think the performance differences are interesting, but how much of the differences are irrelevant when looking at modern drives with tagged queuing, large I/O caches, and reordered block operations? -- Rick C. Petty
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