From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <51DD1A8E.9080702@redhat.com> Date: Wed, 10 Jul 2013 10:25:50 +0200 From: Zdenek Kabelac MIME-Version: 1.0 References: <731d217f00b6d8f6c16a75cbe167baed.squirrel@mail.mohawksoft.com> <51DAF9AF.900@redhat.com> <51DB0CF6.7070400@redhat.com> In-Reply-To: Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] Snapshots of snapshots are not supported yet 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"; format="flowed" To: markw@mohawksoft.com Cc: LVM general discussion and development Dne 10.7.2013 05:45, markw@mohawksoft.com napsal(a): > One more annoying question, if you have the patience. > > Suppose I create a thin provisioned volume, say disk0. > > I take a snapshot of disk0 and name it disk0_snap0 > After a number of changes I then take another snapshot, and call it > disk0_snap1 > > Is the thin provisioning stuff smart enough to realize that disk0_snap0 > should be rewired to reference disk0_snap1 as its origin? It would look > like this: > > disk0 -> disk0_snap1 -> disk0_snap0 > > What I would like to see is something like this: > > disk0 -> disk0_snap2 -> disk0_snap1 -> disk0_snap0 > > Create disk0_snap3 > > disk0 -> disk0_snap3 -> disk0_snap2 -> disk0_snap1 -> disk0_snap0 > > Where all writes to disk0 result in CoW to disk0_snap3 and the remaining > snaps remain unchanged. > > Here is the kicker, I want to perform a differential backup on disk0_snap3 > and disk0_snap2. Suppose I already recreated disk0_snap2 on some server. > I now want to update it to disk0_snap3. I need to get a block list from > disk0_snap2 and disk0_snap3, then generate a list of blocks needed to > permute snap2 to snap3. > > Any info? > Yes - differential snapshot will be supported through thin provisioning target - where you will be able to make a simple diff just by reading metadata - it will be essential piece of replication. AFAIK Joe has this in plan for some time - and there was even some announcement from some third-party developer to support this. There is not going to be any upstream support for doing this with old-snaps in foreseeable future. Also keep in mind your idea of using old-snap of snap of snap would be very slow and fragile to use. Zdenek