Date: Mon, 26 Jul 2010 12:04:34 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-stable@freebsd.org Subject: Re: gpart -b 34 versus gpart -b 1024 Message-ID: <i2jmji$jjm$1@dough.gmane.org> In-Reply-To: <4C4BB672.3090109@langille.org> References: <4C4BA50B.6050507@langille.org> <4C4BB672.3090109@langille.org>
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On 25.7.2010 5:58, Dan Langille wrote: >> -------Sequential Output-------- ---Sequential Input-- --Random-- >> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks--- >> GB M/sec %CPU M/sec %CPU M/sec %CPU M/sec %CPU M/sec %CPU /sec %CPU >> 5 110.6 80.5 115.3 15.1 60.9 8.5 68.8 46.2 326.7 15.3 469 1.4 >> 5 130.9 94.2 118.3 15.6 61.1 8.5 70.1 46.8 241.2 12.7 473 1.4 > 50 113.1 82.4 114.6 15.2 63.4 8.9 72.7 48.2 142.2 9.5 126 0.7 > 50 110.5 81.0 112.8 15.0 62.8 9.0 72.9 48.5 139.7 9.5 144 0.9 > Here, the results aren't much better either... am I not aligning this > partition correctly? Missing something else? Or... are they both 4K > block aligned? As others have said - your drives probably don't have the alignment requiremnt, but your posts show in an excellent example why benchmarking file systems is complicated and how easy it is to measure noise instead of the real thing. To measure real performance in your case, you would either need to benchmark at a layer beneath the file system or with a simple file system which does alwasy predictable io patterns. It's hard to do with zfs with raidz - afaik even accessing the "raw" zvols translates into complex IOs (they are COW).
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