From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 16 May 2016 14:55:19 -0400 From: Mike Snitzer Message-ID: <20160516185518.GA3320@redhat.com> References: <5735AEE4.4080402@assyoma.it> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5735AEE4.4080402@assyoma.it> Subject: Re: [linux-lvm] Backup superblock for thin provision? Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Gionatan Danti Cc: LVM general discussion and development On Fri, May 13 2016 at 6:39am -0400, Gionatan Danti wrote: > Hi all, > using thin provisioning in production machines (using it mostly for > its fast snapshot support, rather than for thin provision / storage > overcommit by itself), I wonder what to do if a critical metadata > corruption, as the loss of the superblock, should happen. > > Filesystems generally have some backup copy of the superblock; > should the primary one fail, another copy can be used. > > So I have the following questions: > - how about thin LVM? Has it a backup superblock somewhere? > - how can the metadata be reliable backupped without shutting down > the volume? > - more generally, how to deal with metadata backup? Does > vgcfgrestore works for thin volumes? > > Thank you all. There is more to the thinp metadata than just the metadata superblock. The DM thin-pool's metadata device was purposely split out from the data device to allow for additional metadata fault protection using RAID. I'll defer to the LVM developers for if/how LVM can be used to have thinp metadata redundancy even if you don't have multiple devices to be able to use a conventional RAID device.