From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 1 Mar 2001 07:18:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 1 Mar 2001 07:17:59 -0500 Received: from zeus.kernel.org ([209.10.41.242]:60377 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id ; Thu, 1 Mar 2001 07:17:53 -0500 Date: Thu, 1 Mar 2001 12:14:18 +0000 From: "Stephen C. Tweedie" To: Martin Rauh Cc: linux-kernel@vger.kernel.org, Stephen Tweedie Subject: Re: Writing on raw device with software RAID 0 is slow Message-ID: <20010301121418.A7647@redhat.com> In-Reply-To: <3A9D1202.9A1C403E@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <3A9D1202.9A1C403E@gmx.de>; from martin.rauh@gmx.de on Wed, Feb 28, 2001 at 03:58:11PM +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Wed, Feb 28, 2001 at 03:58:11PM +0100, Martin Rauh wrote: > > Writing to an software RAID 0 containing 4 SCSI discs is very fast. > I get transfer rates of about 100 MBytes/s. The filesystem on the RAID > is ext2. > > Writing to the same RAID directly (that means on the raw device without > a filesystem) works > but gives low transfer rates of about 31 MBytes/s. > > Any explanation for that? Raw IO is always synchronous: it gets flushed to disk before the write returns. You don't get any write-behind with raw IO, so the smaller the blocksize you write in, the slower things get. --Stephen