From owner-freebsd-hackers@FreeBSD.ORG Fri Jan 18 18:10:13 2013 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 1FE0D5C3; Fri, 18 Jan 2013 18:10:13 +0000 (UTC) (envelope-from wojtek@wojtek.tensor.gdynia.pl) Received: from wojtek.tensor.gdynia.pl (wojtek.tensor.gdynia.pl [188.252.31.196]) by mx1.freebsd.org (Postfix) with ESMTP id 6A9ADD83; Fri, 18 Jan 2013 18:10:12 +0000 (UTC) Received: from wojtek.tensor.gdynia.pl (localhost [127.0.0.1]) by wojtek.tensor.gdynia.pl (8.14.5/8.14.5) with ESMTP id r0IIABSY012651; Fri, 18 Jan 2013 19:10:11 +0100 (CET) (envelope-from wojtek@wojtek.tensor.gdynia.pl) Received: from localhost (wojtek@localhost) by wojtek.tensor.gdynia.pl (8.14.5/8.14.5/Submit) with ESMTP id r0IIABul012648; Fri, 18 Jan 2013 19:10:11 +0100 (CET) (envelope-from wojtek@wojtek.tensor.gdynia.pl) Date: Fri, 18 Jan 2013 19:10:11 +0100 (CET) From: Wojciech Puchar To: Scott Long Subject: Re: IBM blade server abysmal disk write performances In-Reply-To: <1358529778.71931.YahooMailNeo@web120304.mail.ne1.yahoo.com> Message-ID: References: <1358529778.71931.YahooMailNeo@web120304.mail.ne1.yahoo.com> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="2456600518-498302207-1358532611=:12638" X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.2.7 (wojtek.tensor.gdynia.pl [127.0.0.1]); Fri, 18 Jan 2013 19:10:11 +0100 (CET) Cc: "freebsd-hackers@freebsd.org" , Dieter BSD , "gibbs@FreeBSD.org" , "scottl@FreeBSD.org" , "mjacob@FreeBSD.org" X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Jan 2013 18:10:13 -0000 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --2456600518-498302207-1358532611=:12638 Content-Type: TEXT/PLAIN; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8BIT > > The default value, -1, instructs the driver to leave the STA drives at their configuration default.  Often times this means that the MPT BIOS will turn off the write cache on every system boot sequence.  IT DOES THIS FOR A GOOD REASON!  An enabled write cache is counter to data reliability.  Yes, it helps make benchmarks look really good, and it's acceptable if your data can be safely thrown away (for example, you're just caching from a slower source, and the cache can be rebuilt if it gets corrupted).  And yes, Linux has many tricks to make this benchmark look really good.  The tricks range from buffering the raw device to having 'dd' recognize the requested task and short-circuit the process of going to /dev/null or pulling from /dev/zero.  I can't tell you how bogus these tests are and how completely irrelevant they are in predicting actual workload performance.  But, I'm not going to stop anyone from trying, so give the above tunable a try > and let me know how it works. > If computer have UPS then write caching is fine. even if FreeBSD crash, disk would write data --2456600518-498302207-1358532611=:12638--