Date: Wed, 29 Sep 2010 21:10:44 +0300 From: Andriy Gapon <avg@freebsd.org> To: Steven Hartland <killing@multiplay.co.uk> Cc: freebsd-fs@freebsd.org Subject: Re: zfs very poor performance compared to ufs due to lack of cache? Message-ID: <4CA38124.60902@freebsd.org> In-Reply-To: <4C98BFCE.2020202@freebsd.org> References: <5DB6E7C798E44D33A05673F4B773405E@multiplay.co.uk><4C8D087B.5040404@freebsd.org><03537796FAB54E02959E2D64FC83004F@multiplay.co.uk><4C8D280F.3040803@freebsd.org><3FBF66BF11AA4CBBA6124CA435A4A31B@multiplay.co.uk><4C8E4212.30000@freebsd.org> <B98EBECBD399417CA5390C20627384B1@multiplay.co.uk> <D79F15FEB5794315BD8668E40B414BF0@multiplay.co.uk> <4C90B4C8.90203@freebsd.org> <6DFACB27CA8A4A22898BC81E55C4FD36@multiplay.co.uk> <4C90D3A1.7030008@freebsd.org> <0B1A90A08DFE4ADA9540F9F3846FDF38@multiplay.co.uk> <4C90EDB8.3040709@freebsd.org> <3F29E8CED7B24805B2D93F62A4EC9559@multiplay.co.uk> <4C9126FB.2020707@freebsd.org> <1E0B9C1145784776A773B99FC1139CD5@multiplay.co.uk> <4C987F90.6000006@freebsd.org> <4C98803F.7000901@freebsd.org> <879BF5981D1B4C7290BDF18286BA1EEC@multiplay.co.uk> <4C989201.2 0506@freebsd.org> <A77828512281413B8B38EF02732D081C@multiplay.co.uk> <4C98A2BA.1080004@freebsd.org> <EAA0054303614AB2A8CB8863BD54F68C@multiplay.co.uk> <4C98BFCE.2020202@freebsd.org>
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[ping] on 21/09/2010 17:23 Andriy Gapon said the following: > on 21/09/2010 16:53 Steven Hartland said the following: >> That's what I thought you where saying. Is there a test you would suggest to confirm >> either way more accurately? > > Perhaps you can try the test scenario that you described and monitor parameters > suggested by Wiktor in this thread. > > That is, have two large files and set arc max size such that one of them can fit > in ARC readily, but two of them won't fit by a large margin. Make sure that > remaining RAM is large enough to hold both files in page cache. > > 1. sendfile one file, then the other > 2. record kstat.zfs.misc.arcstats values > 3. sendfile the first file again > 4. record kstat.zfs.misc.arcstats values > > If the first file data was re-used from page cache, then you won't see much > changes in kstat.zfs.misc.arcstats. If it had to be taken from ARC or from disk, > then either ARC hits or ARC misses will grow noticeably. > > Make sure to not have any parallel activity that could affect kstat.zfs.misc.arcstats. > > I think kstat.zfs.misc.arcstats.hits and kstat.zfs.misc.arcstats.misses are two > primary indicators in this test. > -- Andriy Gapon
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