From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43782) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fG3oa-0001Pw-5C for qemu-devel@nongnu.org; Tue, 08 May 2018 10:42:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fG3oX-0002Dl-21 for qemu-devel@nongnu.org; Tue, 08 May 2018 10:42:04 -0400 References: <1514187226.13662.28.camel@intel.com> From: Eric Blake Message-ID: <6e792b9f-2281-e8db-0410-c4c3468ffc90@redhat.com> Date: Tue, 8 May 2018 09:41:40 -0500 MIME-Version: 1.0 In-Reply-To: <1514187226.13662.28.camel@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] Some question about savem/qcow2 incremental snapshot List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: He Junyan , qemu-devel@nongnu.org, John Snow , qemu block On 12/25/2017 01:33 AM, He Junyan wrote: > hi all: >=20 > I am now focusing on snapshot optimization for Intel NVDimm kind > memory. Different from the normal memory, the NVDimm may be 128G, 256G > or even more for just one guest, and its speed is slower than the > normal memory. So sometimes it may take several minutes to complete > just one snapshot saving. Even with compression enabled, the=C2=A0snaps= hot > point may consume more than 30G disk space. > We decide to add incremental kind snapshot saving to resolve this. Just > store difference between snapshot points to save time and disk space. > But the current snapshot/save_vm framework seems not to support this. > We need to add snapshot dependency and extra operations when we LOAD > and DELETE the snapshot point. > Is that possible to modify the savevm framework and add some > incremental snapshot support to QCOW2 format? In general, the list has tended to focus on external snapshots rather=20 than internal; where persistent bitmaps have been the proposed mechanism=20 for tracking incremental differences between snapshots. But yes, it is=20 certainly feasible that patches to improve internal snapshots to take=20 advantage of incremental relationships may prove useful. You will need=20 to document all enhancements to the qcow2 file format and get that=20 approved first, as interoperability demands that others reading the same=20 spec would be able to interpret the image you create that is utilizing=20 an internal snapshot with an incremental diff. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org