From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Grant Grundler" Subject: Re: weird throughput on write to SATA disk Date: Mon, 13 Oct 2008 14:34:00 -0700 Message-ID: References: <1223925629.3947.7.camel@duo> <1223932956.3947.22.camel@duo> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-out.google.com ([216.239.33.17]:59681 "EHLO smtp-out3.google.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752425AbYJMVeS (ORCPT ); Mon, 13 Oct 2008 17:34:18 -0400 In-Reply-To: <1223932956.3947.22.camel@duo> Content-Disposition: inline Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: kenneth johansson Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Oct 13, 2008 at 2:22 PM, kenneth johansson wrote: > On Mon, 2008-10-13 at 14:07 -0700, Grant Grundler wrote: >> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson wrote: >> > When writing data to /dev/sdb (that is the whole disk and no filesystem) >> > it starts out ok around 100MB/sec but soon end up doing considerably >> > worse. For prolonged times lasting several minutes it hovers in the >> > 20-30MB/sec. >> >> Is the application using "O_DIRECT"? > > no just open then write no fancy stuff > >> If not, could be issue with how VM writeback is (not) working. > > the access pattern is the simplest possible. Is there any knobs I could > try to adjust. > >> Can you reproduce this using fio or even "dd"? >> (See git://git.kernel.dk/fio) > > dd is having the same effect. Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? Or try with "sgp_dd"? It's part of sg3-utils package. thanks, grant