From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wido den Hollander Subject: RBD performance with many childs and snapshots Date: Mon, 21 Dec 2015 20:06:17 +0100 Message-ID: <56784DA9.9060304@42on.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from smtp02.mail.pcextreme.nl ([109.72.87.139]:45865 "EHLO smtp02.mail.pcextreme.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751611AbbLUTGW (ORCPT ); Mon, 21 Dec 2015 14:06:22 -0500 Received: from [192.168.8.128] (cable-178-107.zeelandnet.nl [82.176.178.107]) by smtp02.mail.pcextreme.nl (Postfix) with ESMTPSA id 940D34007F for ; Mon, 21 Dec 2015 20:06:17 +0100 (CET) Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel Hi, While implementing the buildvolfrom method in libvirt for RBD I'm stuck at some point. $ virsh vol-clone --pool myrbdpool image1 image2 This would clone image1 to a new RBD image called 'image2'. The code I've written now does: 1. Create a snapshot called image1@libvirt- 2. Protect the snapshot 3. Clone the snapshot to 'image1' wido@wido-desktop:~/repos/libvirt$ ./tools/virsh vol-clone --pool rbdpool image1 image2 Vol image2 cloned from image1 wido@wido-desktop:~/repos/libvirt$ root@alpha:~# rbd -p libvirt info image2 rbd image 'image2': size 10240 MB in 2560 objects order 22 (4096 kB objects) block_name_prefix: rbd_data.1976451ead36b format: 2 features: layering, striping flags: parent: libvirt/image1@libvirt-1450724650 overlap: 10240 MB stripe unit: 4096 kB stripe count: 1 root@alpha:~# But this could potentially lead to a lot of snapshots with children on 'image1'. image1 itself will probably never change, but I'm wondering about the negative performance impact this might have on a OSD. I'd rather not hardcode a snapshot name like 'libvirt-parent-snapshot' into libvirt. There is however no way to pass something like a snapshot name in libvirt when cloning. Any bright suggestions? Or is it fine to create so many snapshots? -- Wido den Hollander 42on B.V. Ceph trainer and consultant Phone: +31 (0)20 700 9902 Skype: contact42on