From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49082) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gKOwu-0006XZ-EE for qemu-devel@nongnu.org; Wed, 07 Nov 2018 09:36:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gKOwt-0008WS-B7 for qemu-devel@nongnu.org; Wed, 07 Nov 2018 09:36:52 -0500 Date: Wed, 7 Nov 2018 14:36:28 +0000 From: "Richard W.M. Jones" Message-ID: <20181107143628.GG8125@redhat.com> References: <20181107121319.GC14842@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181107121319.GC14842@redhat.com> Subject: Re: [Qemu-devel] Change in qemu 2.12 causes qemu-img convert to NBD to write more data List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, eblake@redhat.com, qemu-block@nongnu.org, Edgar Kaziakhmedov Cc: nsoffer@redhat.com Another thing I tried was to change the NBD server (nbdkit) so that it doesn't advertise zero support to the client: $ nbdkit --filter=log --filter=nozero memory size=6G logfile=/tmp/log \ --run './qemu-img convert ./fedora-28.img -n $nbd' $ grep '\.\.\.$' /tmp/log | sed 's/.*\([A-Z][a-z]*\).*/\1/' | uniq -c 2154 Write Not surprisingly no zero commands are issued. The size of the write commands is very uneven -- it appears to be send one command per block of zeroes or data. Nir: If we could get information from imageio about whether zeroing is implemented efficiently or not by the backend, we could change virt-v2v / nbdkit to advertise this back to qemu. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html