Date: Wed, 5 May 2010 07:34:55 -0500 From: Peter Steele <psteele@maxiscale.com> To: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Suspect results from iostat--FBSD bug? Message-ID: <7B9397B189EB6E46A5EE7B4C8A4BB7CB3E0CB171@MBX03.exg5.exghost.com>
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We use iostat to collect statistics of hard drive activity. We've been seei= ng some values for the transaction wait column that look suspicious. This i= s easy to reproduce by just running iostat repeatedly over a short period o= f time, as I show below. Notice the third from last column. From what I und= erstand, when run in this fashion the values displayed are averaged over th= e system uptime. I'd expect then for the transaction wait value to not take= these sudden dips. Is there an explanation for this? # for ((i=3D1; i <=3D100; i++)); do iostat -dxI ad8|tail +3; sleep 5; done ad8 10291.0 569044.0 151986.0 10164944.0 4294967295 47.7 93 ad8 10304.0 570070.0 152012.0 10185395.0 4294967295 47.6 93 ad8 10312.0 571047.0 152028.0 10204575.0 85 47.5 93 ad8 10317.0 571729.0 152038.0 10217633.0 4294967295 47.5 93 ad8 10321.0 572363.0 152046.0 10230152.0 4294967295 47.4 93 ad8 10324.0 573863.0 152052.0 10247668.0 4294967295 48.2 93 ad8 10325.0 574438.0 152054.0 10259296.0 4294967295 48.1 93 ad8 10330.0 575150.0 152078.0 10273362.0 4294967295 48.1 93 ad8 10332.0 575693.0 152082.0 10283567.0 4294967295 48.0 93 ad8 10334.0 576478.0 152086.0 10298971.0 4294967295 48.0 93 ad8 10337.0 577363.0 152092.0 10316766.0 4294967295 47.9 93 ad8 10340.0 578501.0 152098.0 10328958.0 4294967295 48.4 93 ad8 10343.0 579682.0 152104.0 10352494.0 4294967295 48.3 93 ad8 10349.0 580806.0 152116.0 10375251.0 4294967295 48.2 93 ad8 10356.0 581462.0 152200.0 10387402.0 0 48.1 93 ad8 10362.0 582392.0 152212.0 10405738.0 4294967295 48.1 93 ad8 10367.0 583326.0 152222.0 10424055.0 4294967295 48.0 93 ad8 10367.0 584412.0 152222.0 10432981.0 4294967295 48.7 93 ad8 10376.0 585764.0 152240.0 10460020.0 4294967295 48.6 93 ad8 10377.0 586649.0 152242.0 10477525.0 4294967295 48.5 93 ad8 10382.0 587266.0 152252.0 10488950.0 4294967295 48.5 93 ad8 10392.0 587977.0 152272.0 10503115.0 4294967295 48.4 93 ad8 10402.0 588713.0 152292.0 10518177.0 4294967295 48.4 93 ad8 10403.0 589831.0 152294.0 10527746.0 16 48.8 93 ad8 10419.0 590811.0 152326.0 10547455.0 4294967295 48.7 93
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