From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx2.redhat.com (mx2.redhat.com [10.255.15.25]) by int-mx2.corp.redhat.com (8.13.1/8.13.1) with ESMTP id l4D26c4B002161 for ; Sat, 12 May 2007 22:06:40 -0400 Received: from mail.davidb.org (mail.davidb.org [66.93.32.219]) by mx2.redhat.com (8.13.1/8.13.1) with ESMTP id l4D26UOt021902 for ; Sat, 12 May 2007 22:06:33 -0400 Received: from a64.davidb.org ([66.93.32.226]) by mail.davidb.org with esmtpa (Exim 4.62 #1 (Debian)) id 1Hn3Ti-0004I0-Aw for ; Sat, 12 May 2007 19:06:30 -0700 Message-ID: <464672A6.3000408@davidb.org> Date: Sat, 12 May 2007 19:06:30 -0700 From: David Brown MIME-Version: 1.0 Subject: Re: [linux-lvm] LVM on SATA/PATA disks References: In-Reply-To: Content-Transfer-Encoding: 7bit Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" To: LVM general discussion and development Stuart D. Gathman wrote: >> How does SATA fit in with all of this? Is it basically the same >> limitations on the bus as IDE/PATA, so that you'd really not want to put >> more than 1 device per bus? > > SATA mandates at most 1 disk per channel, making the issue moot. It is > still true that there is only one active disk on a bus. But then there > is only one disk on a bus. Newer SATA drives, with proper newer controllers and proper device driver support will support NCQ (native command queueing), which allows the drive to re-order requests. It appears that the Linux ACHI and Nvidia SATA drivers support this capability in recent kernels. Of course, any of the re-ordering (SCSI TCQ, or SATA NCQ) requires filesystem and driver support of write barriers for reliability. Write barriers are not implement in DM, hence LVM, so there is a reliability risk in going with this kind of solution. Depending on the filesystem this can result in power failures resulting in files having inconsistent data. Dave