From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jim Fehlig Subject: Re: [PATCH] vhd-util create: add -C|nocow option Date: Fri, 22 Nov 2013 09:09:59 -0700 Message-ID: <528F81D7.4010902@suse.com> References: <1385019976-19885-1-git-send-email-cyliu@suse.com> <1385026779.6071.112.camel@kazak.uk.xensource.com> <21134.7091.735293.78218@mariner.uk.xensource.com> <528EAC02.9010009@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Chunyan Liu Cc: "xen-devel@lists.xensource.com" , Ian Jackson , Ian Campbell List-Id: xen-devel@lists.xenproject.org Chunyan Liu wrote: > > > > 2013/11/22 Jim Fehlig > > > Ian Jackson wrote: > > Ian Campbell writes ("Re: [Xen-devel] [PATCH] vhd-util create: > add -C|nocow option"): > > > >> On Thu, 2013-11-21 at 15:46 +0800, Chunyan Liu wrote: > >> > >>> Add '-C' (nocow) option to vhd-util create. > >>> > >>> Btrfs has terrible performance when hosting VM images, even > more when the guest > >>> in those VM are also using btrfs as file system. One way to > mitigate this bad > >>> performance is to turn off COW attributes on VM files (since > having copy on > >>> write for this kind of data is not useful). According to > 'chattr' manpage, NOCOW > >>> could be set to new or empty file only on btrfs, so add a > option here so that > >>> users could have a chance to set NOCOW to a vhd image. > >>> > >> Is there not some btrfs (or generic) utility which could be > used to do > >> this after image creation rather than trying to build it in to > every > >> utility which creates an image file? > >> > > > > This may seem like a daft question, but why do we even have a vhd > > utility in our tree ? Is there not some vhd tools package that this > > should be in ? > > > > Newer qemu-img supports vhd and vhdx right? Is there even a need for > this tool at all anymore? > > > 'qemu-img create' doesn't support creating vhd/vhdx format images. > Only open/probe supported. Ah, I didn't know that. Is it possible to merge vhd-util with qemu-img? You could then support nocow with something like 'qemu-img create -f vhd -o nocow, ...'. But I tend to agree with Ian that supporting backing store-specific features should be higher in the stack. E.g. a libvirt filesystem storage pool of type btrfs could support such features when creating volumes from the pool. Regards, Jim