From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55325) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VkyR2-0004AX-GV for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:50:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VkyQw-0007R1-Io for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:50:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45236) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VkyQw-0007Qw-7v for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:50:46 -0500 Message-ID: <529371CF.3030507@redhat.com> Date: Mon, 25 Nov 2013 16:50:39 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1385387840-17307-1-git-send-email-pl@kamp.de> <1385387840-17307-6-git-send-email-pl@kamp.de> <529368A8.8050807@redhat.com> <52936D8C.50709@kamp.de> In-Reply-To: <52936D8C.50709@kamp.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1.8 5/6] qemu-img: add option to align writes to cluster_sectors during convert List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com Il 25/11/2013 16:32, Peter Lieven ha scritto: >> >> Also, a couple of ideas for separate patches. Perhaps the default value >> of "-S" could be cluster_size if specified? This would avoid making raw >> images too fragmented, and compounding filesystem-level fragmentation >> with qcow2-level fragmentation. And 4K is too small a default in my >> opinion; it could be easily changed to 64K, though 4K was of course an >> improvement compared to 512 before commit a22f123 (qemu-img: Require >> larger zero areas for sparse handling, 2011-08-26). > I would vote for 64K or 256K, we already use the first for some time. > However, it turned out > that (much) bigger values decrease performance. Setting it > to cluster_size can be dangerous. As described in my case its 15MB and > I think for vhd its 1MB. This can be a lot of zeros that have to be > written. What about max(4096, min(bdi->cluster_size, 1048576))? Paolo