From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55651) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VgtTm-0002gM-KA for qemu-devel@nongnu.org; Thu, 14 Nov 2013 04:44:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VgtTh-0006Gj-IP for qemu-devel@nongnu.org; Thu, 14 Nov 2013 04:44:50 -0500 Received: from static.88-198-71-155.clients.your-server.de ([88.198.71.155]:49947 helo=socrates.bennee.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VgtTh-0006GJ-Bt for qemu-devel@nongnu.org; Thu, 14 Nov 2013 04:44:45 -0500 References: <1384416928-3441-1-git-send-email-cyliu@suse.com> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <1384416928-3441-1-git-send-email-cyliu@suse.com> Date: Thu, 14 Nov 2013 09:44:42 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] qemu-img: set nocow flag to new file List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Chunyan Liu Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com cyliu@suse.com writes: > Set NOCOW flag to newly created images to solve performance issues on btrfs. > > 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). It's been a while since I had to mess with this performance mystery but I recall you also need to ensure the partition needs to be mounted with the nodatacow mount option. Unless this has changed we should probably warn the user about that. -- Alex Bennée