Date: Fri, 18 Apr 2008 13:45:40 +0100 From: Stephane Chazelas Subject: Re: [linux-lvm] snapshotting to a different volume group Message-ID: References: <20080418082436.GA7331@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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: mauelshagen@redhat.com, LVM general discussion and development 2008-04-18 12:53:15 +0100, Stephane Chazelas: [...] > By bypassing LVM2 and using dmsetup directly, would I > theoretically be able to setup a snapshot outside of LVM2 > managed volume groups, is it worth me trying to dig that way? > Something like: having a LVM (or not) volume group with only > /dev/md0 and creating snapshots of that elsewhere while leaving > the VG containing /dev/md0 undisturbed? [...] [replying to myself] OK, I get it. When one creates a snapshot, he changes the original block device to be a "snapshot-origin" so that every write to the device is forked into: - copying the original block to the snapshot device(s) COW(s) - writing to the original device. So, if I've got the COWs on a failed disk, I suspect this might degrade the performances or even stop the snapshot-origin from working altogether wouldn't it? I'll keep testing... -- Stephane