From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Mcx8K-0000wP-SR for qemu-devel@nongnu.org; Mon, 17 Aug 2009 04:00:00 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Mcx8F-0000w6-JX for qemu-devel@nongnu.org; Mon, 17 Aug 2009 03:59:59 -0400 Received: from [199.232.76.173] (port=49358 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Mcx8F-0000w3-Dl for qemu-devel@nongnu.org; Mon, 17 Aug 2009 03:59:55 -0400 Received: from mx20.gnu.org ([199.232.41.8]:43090) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Mcx8E-0000ib-NJ for qemu-devel@nongnu.org; Mon, 17 Aug 2009 03:59:54 -0400 Received: from mx2.redhat.com ([66.187.237.31]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1Mcx8B-000332-FI for qemu-devel@nongnu.org; Mon, 17 Aug 2009 03:59:51 -0400 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n7H7xoHX029040 for ; Mon, 17 Aug 2009 03:59:50 -0400 Message-ID: <4A890DB4.8060609@redhat.com> Date: Mon, 17 Aug 2009 09:58:44 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] qcow2: Metadata preallocation References: <1250262015-996-1-git-send-email-kwolf@redhat.com> <4A87F44B.5080308@redhat.com> <4A8902AA.2050200@redhat.com> <4A890A9D.4070000@redhat.com> In-Reply-To: <4A890A9D.4070000@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: qemu-devel@nongnu.org Avi Kivity schrieb: >> Even with improved concurrent cluster allocation, you might profit from >> metadata preallocation by having less fragmented qcow2 images which >> avoids splitting up requests. Not sure if this is relevant in practice >> though. > > What I meant was that I prefer changes that improve performance > throughout the lifetime of the image rather than the initial writes, > especially as there's a space tradeoff. Avoiding fragmentation could improve performance during normal operation (that is, as long as you don't use snapshots). And I wouldn't worry about the space tradeoff: Metadata for a 10 GB image is under 2 MB, and a good part of it would be needed anyway. But I completely agree that it is not the solution to all of our problems. Kevin