From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: raw disks no longer work in latest kvm (kvm-88 was fine) Date: Sun, 07 Mar 2010 21:12:37 +0200 Message-ID: <4B93FAA5.6010803@redhat.com> References: <4B92BF97.4040001@nagafix.co.uk> <4B92C90B.4030807@msgid.tls.msk.ru> <4B932829.8090503@nagafix.co.uk> <4B9372B6.3050408@msgid.tls.msk.ru> <20100307100022.GA23201@infradead.org> <4B93A624.8010707@nagafix.co.uk> <4B93AF8A.3070805@nagafix.co.uk> <4B93C2F9.7030904@msgid.tls.msk.ru> <4B93DE3F.4090103@nagafix.co.uk> <4B93DFF0.5050905@redhat.com> <20100307172151.GA24859@infradead.org> <4B93E29E.6090609@redhat.com> <4B93E9EE.6020701@nagafix.co.uk> <4B93F4A4.9050003@redhat.com> <4B93F9E6.2050301@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Antoine Martin , Christoph Hellwig , Michael Tokarev , kvm@vger.kernel.org To: Asdo Return-path: Received: from mx1.redhat.com ([209.132.183.28]:34123 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997Ab0CGTMx (ORCPT ); Sun, 7 Mar 2010 14:12:53 -0500 In-Reply-To: <4B93F9E6.2050301@shiftmail.org> Sender: kvm-owner@vger.kernel.org List-ID: On 03/07/2010 09:09 PM, Asdo wrote: > Avi Kivity wrote: >> On 03/07/2010 08:01 PM, Antoine Martin wrote: >>> >>> Yes cache=none: "-drive file=./vm/var_fs,if=virtio,cache=none" >>> >>> Side question: this is the right thing to do for raw partitions, right? >> >> The rightest. > > Isn't cache=writeback now safe on virtio-blk since 2.6.32? Yes. > Doesn't it provide better performances? No. The guest will do its own caching, so unless the guest is really short of memory, you aren't gaining much; and the copying will hurt. > > Also that looks like a raw file to me, not a partition... do they > follow the same optimization "rule"? More or less. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.