From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f41.google.com ([209.85.213.41]:48456 "EHLO mail-yh0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054AbaKZFL3 (ORCPT ); Wed, 26 Nov 2014 00:11:29 -0500 Received: by mail-yh0-f41.google.com with SMTP id a41so999835yho.0 for ; Tue, 25 Nov 2014 21:11:28 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <27BDAC3B-789C-4477-B065-E703CE425F54@colorremedies.com> <546B68F8.6080008@ubuntu.com> <546BA96D.4050805@ubuntu.com> <2A57F99C-80AA-4FD4-AA41-57F02AD4E1A2@colorremedies.com> <546CB531.2060509@ubuntu.com> <20141121042814.GR17395@hungrycats.org> <5470C92E.1070607@inwind.it> <20141123001927.GO17380@hungrycats.org> <5474AF87.6090702@inwind.it> <20141125202948.GP17380@hungrycats.org> <5474FBD9.5070709@inwind.it> Date: Tue, 25 Nov 2014 22:11:28 -0700 Message-ID: Subject: Re: BTRFS messes up snapshot LV with origin From: Chris Murphy To: Btrfs BTRFS Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Nov 25, 2014 at 8:22 PM, Duncan <1i5t5.duncan@cox.net> wrote: > From my perspective, however, btrfs is simply incompatible with lvm > snapshots, because the basic assumptions are incompatible. Btrfs assumes > UUIDs will be exactly what they say on the label, /unique/, while lvm's > snapshot feature directly breaks that uniqueness by copying the (former) > UUID, thus making the former UUID no longer unique and thus no longer > truly UUID. The seed device has a mechanism to change volume UUID without rewriting a bunch of stuff in the original, the gotcha is that it requires adding a device. man fsfreeze says "fsfreeze is unncessary for device-mapper devices. The device-mapper (and LVM) automatically freezes filesystem on the device when a snapshot creation is requested." So if it's possible to communicate snapshotting/freezing to the fs at snapshot time, then maybe btrfs could 'btrfstune -S 1' the volume in the snapshot. That way that snapshot actually contains a btrfs seed device, which is read only. At least the snapshot copy isn't going to get obliterated in an accident; even though most people would probably want the origin LV to be protected while considering the snapshot disposable. -- Chris Murphy