From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [Qemu-devel] KVM call agenda for October 25 Date: Wed, 26 Oct 2011 11:41:52 +0200 Message-ID: <4EA7D5E0.7070101@redhat.com> References: <4EA6ACFE.6090109@redhat.com> <4EA6B41B.3000903@codemonkey.ws> <4EA6C00B.3030701@redhat.com> <4EA6C25C.8000502@codemonkey.ws> <4EA7C1B8.9000903@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , Anthony Liguori , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Markus Armbruster Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33055 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932616Ab1JZJl6 (ORCPT ); Wed, 26 Oct 2011 05:41:58 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 10/26/2011 10:48 AM, Markus Armbruster wrote: > Sector size is a device property. > > If the user asks for a 4K sector disk, and the backend can't support > that, we need to reject the configuration. Just like we reject > read-only backends for read/write disks. Isn't it the other way round, i.e. the user asks for a 512-byte sector disk (i.e. the default) with cache=none but the disk has 4k sectors? We're basically saying "choose between NFS and migration if you have 4k sector disks but your guest doesn't support them". Understandable perhaps, but not exactly kind, and virtualization is also about shielding from this kind of hardware dependency even at the cost of performance. QEMU should just warn about performance degradations, erroring out would be a policy decision that should be up to management. > It's okay to default device properties to some backend-dependent value, > if that improves usability. On the other hand, not all guests support 4k-sectors properly. Paolo