From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4797686A.4000306@wpkg.org> Date: Wed, 23 Jan 2008 17:16:42 +0100 From: Tomasz Chmielewski MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [linux-lvm] Re: [RFC] Multiple Snapshots - Manageability problem 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: linux-lvm@redhat.com, mvijai@novell.com, dm-devel@redhat.com Vijai Babu Madhavan, Thu, 11 Jan 2007 11:18:13 -0700, wrote: > The problem of DM snapshots with multiple snapshots have been discussed > in the lists quiet a bit (Most recently @ > https://www.redhat.com/archives/dm-devel/2006-October/msg00034.html). > > We are currently in the process of building a DM snapshot target that scales > well with many snapshots (so that the changed blocks don't get copied to each > snapshot). In this process, I would also like to validate an assumption. > > Today, when a single snapshot gets created, a new cow device of a given size > is also created. IMO, there are two problems with this approach: > > a) It is difficult to predict the size of the cow device, which requires a prediction > of the number of writes would go into the origin volume during the snapshot > life cycle. It is difficult to get this prediction right, as very high value reduces > utilization and low value increases the chances of snapshot becoming full. > > b) A new cow device needs to be created every time. Hi, Any news on that? Still, with multiple snapshots write performance degrades linearly - is any work done to change that anytime soon? -- Tomasz Chmielewski http://wpkg.org