Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757541AbXKKSdq (ORCPT ); Sun, 11 Nov 2007 13:33:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753541AbXKKSdi (ORCPT ); Sun, 11 Nov 2007 13:33:38 -0500 Received: from eazy.amigager.de ([213.239.192.238]:60626 "EHLO eazy.amigager.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751974AbXKKSdh (ORCPT ); Sun, 11 Nov 2007 13:33:37 -0500 Date: Sun, 11 Nov 2007 19:33:35 +0100 From: Tino Keitel To: linux-kernel@vger.kernel.org Subject: Strage buffer behaviour Message-ID: <20071111183334.GA6770@dose.home.local> Mail-Followup-To: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1764 Lines: 51 Hi folks, I noticed that the kernel (2.6.23.1) seems to buffer only certain partitions on my system: $ for i in 1 2 3 4 ; do for j in 1 2 ; do dd if=/dev/sda$i of=/dev/null bs=1024k count=100 ; done ; done 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 3.01471 seconds, 34.8 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 2.86945 seconds, 36.5 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 2.92038 seconds, 35.9 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 3.00272 seconds, 34.9 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 4.07722 seconds, 25.7 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 0.0944248 seconds, 1.1 GB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 5.61527 seconds, 18.7 MB/s 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 0.331822 seconds, 316 MB/s The dd command reads 100 MB from each partition two times in a row. It looks like sda1 and sda2 are not bufferd (the first 4 dd runs), but sda3 and sda4 are (the last 4 dd runs). The computer is a Mac mini with a 2,5" SATA hard disk. The first 2 partitions contain EFI and MacOS X, and are unused in Linux. The last 2 partitions are an ext3 partition for / and an LVM for the rest of the sytem. Any hints how the dd/buffering behaviour could be explained? The system was mostly idle, and the numbers are reproducible across reboots. Regards, Tino - 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/