Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932116AbWCXPtO (ORCPT ); Fri, 24 Mar 2006 10:49:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751137AbWCXPtN (ORCPT ); Fri, 24 Mar 2006 10:49:13 -0500 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:58776 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1751130AbWCXPtK (ORCPT ); Fri, 24 Mar 2006 10:49:10 -0500 Subject: Re: [RFC PATCH 35/35] Add Xen virtual block device driver. From: Alan Cox To: Jeff Garzik Cc: Ian Pratt , Anthony Liguori , Chris Wright , virtualization@lists.osdl.org, xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org, Ian Pratt , ian.pratt@cl.cam.ac.uk, SCSI Mailing List In-Reply-To: <4423E853.1040707@garzik.org> References: <4421D943.1090804@garzik.org> <1143202673.18986.5.camel@localhost.localdomain> <4423E853.1040707@garzik.org> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Fri, 24 Mar 2006 15:55:27 +0000 Message-Id: <1143215728.18986.15.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1265 Lines: 33 On Gwe, 2006-03-24 at 07:38 -0500, Jeff Garzik wrote: > > A pure SCSI abstraction doesn't allow for shared head scheduling which > > you will need to scale Xen sanely on typical PC boxes. > > Not true at all. If you can do it with a block device, you can do it > with a SCSI block device. I don't believe this is true. The complexity of expressing sequences of command ordering between virtual machines acting in a co-operative but secure manner isn't as far as I can see expressable sanely in SCSI TCQ > > In fact, SCSI should make a few things easier, because the notion of > host+bus topology is already present, and notion of messaging is already > present, so you don't have to recreate that in a Xen block device > infrastructure. Those are the easy bits. > > are also always full of bits people got wrong, often critical bits like > > tagged queues and error sequences - things that break your journalled > > file system. > > This I'll grant you. And every one you get wrong is a corruptor.... Alan - 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/