Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755414AbYJNBe1 (ORCPT ); Mon, 13 Oct 2008 21:34:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752495AbYJNBeS (ORCPT ); Mon, 13 Oct 2008 21:34:18 -0400 Received: from smtp-out.google.com ([216.239.33.17]:25209 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752068AbYJNBeR (ORCPT ); Mon, 13 Oct 2008 21:34:17 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=message-id:date:from:to:subject:cc:in-reply-to: mime-version:content-type:content-transfer-encoding: content-disposition:references; b=VsyIgdlGeNEMKRNfySuCJ/vND0bnaSwryIOef5Sy9/ABWpOBWQE+zKN0mLsaXP/VP tLnGZ+IYIX/6a3OKlNYtA== Message-ID: Date: Mon, 13 Oct 2008 18:33:55 -0700 From: "Grant Grundler" To: "kenneth johansson" Subject: Re: weird throughput on write to SATA disk Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <1223936351.3947.41.camel@duo> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1223925629.3947.7.camel@duo> <1223932956.3947.22.camel@duo> <1223936351.3947.41.camel@duo> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1225 Lines: 31 On Mon, Oct 13, 2008 at 3:19 PM, kenneth johansson wrote: ... >> Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? > > I changed to use O_DIRECT and it's much more consistent now. 69-75 with > 74 about 95% of the time. That's low but it could be worse. Many things can contribute to slow disks. Favorites are overtemp (See SMART field 194) and vibration (no measurement possible w/o special equipment). "dd" isn't exactly a performance application until one uses really big block sizes (1MB or larger). sgp_dd is better since it is multi-threaded. fio has all the right knobs to test disk perf and measure it properly. > the disk is supposed to have 105 115 sustained > data rate. Where did 105-115 number come from? The best I've seen to date with 7200 rpm drives was 108MB/s on the outside diameter. That degrades slowly until about 60-70% towards the inside diameter and then drops off dramatically (down to something like 50MB/s). hth, grant -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/