From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [RFC PATCH 35/35] Add Xen virtual block device driver. Date: Sat, 25 Mar 2006 21:03:11 +1100 Message-ID: <1143280992.8228.12.camel@localhost.localdomain> References: <4421D943.1090804@garzik.org> <1143202673.18986.5.camel@localhost.localdomain> <4423E853.1040707@garzik.org> <1143215728.18986.15.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1143215728.18986.15.camel@localhost.localdomain> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Alan Cox Cc: xen-devel@lists.xensource.com, Jeff Garzik , SCSI Mailing List , virtualization@lists.osdl.org, linux-kernel@vger.kernel.org, Chris Wright , Ian Pratt List-Id: linux-scsi@vger.kernel.org On Fri, 2006-03-24 at 15:55 +0000, Alan Cox wrote: > 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 I thought usb_scsi taught us that SCSI was overkill for a block abstraction? I have a much simpler Xen block-device implementation which seems to perform OK, and is a lot less LOC than the in-tree one, so I don't think the "SCSI would be better than what's there" (while possibly true) is valid. Cheers! Rusty. -- ccontrol: http://ozlabs.org/~rusty/ccontrol