From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751128AbWGPQi0 (ORCPT ); Sun, 16 Jul 2006 12:38:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751129AbWGPQi0 (ORCPT ); Sun, 16 Jul 2006 12:38:26 -0400 Received: from wr-out-0506.google.com ([64.233.184.226]:3140 "EHLO wr-out-0506.google.com") by vger.kernel.org with ESMTP id S1751128AbWGPQiZ (ORCPT ); Sun, 16 Jul 2006 12:38:25 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=NbqeXLvAMe8qY4+YdfGFGUNlZtFme5jL3UGa5EBSbpOmx6w08p5Lr2GXEcsdzdmYYm/D+ZeW2ijgkJOIv1vNzIgbZivRPc3ETsZ3hObqU7+qUL7mQHPyPdYERzrG52ZhZIBHXiZ2IVy4CbKlY1KkTb9DcHl3kzqKXKWLltLd1cw= Message-ID: Date: Sun, 16 Jul 2006 09:38:25 -0700 From: "Jonathan Baccash" To: "Avi Kivity" Subject: Re: raid io requests not parallel? Cc: linux-kernel@vger.kernel.org In-Reply-To: <44B9D2CA.8040306@argo.co.il> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <44B9D2CA.8040306@argo.co.il> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Each head has to service 1024 write requests (compared to just 512 read > requests). By that logic, it would take twice as long for my writes to finish. Why is it taking 4x as long in my parallel test? I don't think any of the repliers understood my question. What I want to know is, during a single direct IO write request, I would expect the raid software to issue the write request to both disks simultaneously. But the evidence indicates that isn't what is happening. I would expect a raid-1 write to take about as long to write a single block as a single write to a single disk (assuming no other disk activity), because I would expect two writes to happen concurrently.