From owner-freebsd-stable@freebsd.org Fri Nov 27 04:46:49 2015 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id D62F4A36F13 for ; Fri, 27 Nov 2015 04:46:49 +0000 (UTC) (envelope-from emz@norma.perm.ru) Received: from elf.hq.norma.perm.ru (unknown [IPv6:2a00:7540:1::5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mail.norma.perm.ru", Issuer "Vivat-Trade UNIX Root CA" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 427F915EB for ; Fri, 27 Nov 2015 04:46:48 +0000 (UTC) (envelope-from emz@norma.perm.ru) Received: from bsdrookie.norma.com. ([IPv6:fd00::77d]) by elf.hq.norma.perm.ru (8.14.9/8.14.9) with ESMTP id tAR4kfoZ005432 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO) for ; Fri, 27 Nov 2015 09:46:41 +0500 (YEKT) (envelope-from emz@norma.perm.ru) From: "Eugene M. Zheganin" Subject: Re: high disk %busy, while almost nothing happens To: freebsd-stable@freebsd.org References: <5656CE96.9000103@norma.perm.ru> Message-ID: <5657E031.4030703@norma.perm.ru> Date: Fri, 27 Nov 2015 09:46:41 +0500 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <5656CE96.9000103@norma.perm.ru> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.4.3 (elf.hq.norma.perm.ru [IPv6:fd00::30a]); Fri, 27 Nov 2015 09:46:41 +0500 (YEKT) X-Spam-Status: No hits=-100.4 bayes=0.0000 testhits AWL=0.007,BAYES_00=-1.9, RDNS_NONE=0.793,SPF_SOFTFAIL=0.665,USER_IN_WHITELIST=-100 autolearn=no autolearn_force=no version=3.4.0 X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on elf.hq.norma.perm.ru X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 27 Nov 2015 04:46:49 -0000 Hi. On 26.11.2015 14:19, Eugene M. Zheganin wrote: > Hi. > > I'm using FreeBSD 10.1-STABLE as an application server, last week I've > noticed that disks are always busy while gstat shows that the activity > measured in iops/reads/writes is low, form my point of view: > > > L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name > 8 56 50 520 160.6 6 286 157.4 100.2 gpt/zfsroot0 > 8 56 51 1474 162.8 5 228 174.4 99.9 gpt/zfsroot1 > > These %busy numbers arent't changing much, and from my point of view > both disks do very little. > The thing is, it was the compression. As soon as I cleared the gzip compression from busy datasets, %busy went down, almost to zero. Affected datasets were filled with poorly compressionable files, mostly archives or zlib-compressed data. And this is kind of counter-intuitive: one could think that worse-case scenario would be redundant CPU load, with constand disk i/o. In practice, otherwise, high disk %busy happens. Could someone explain that ? I only found this because of the flow-capture was starting like for years, and I started to suspect the compression setting. Eugene.