Not quite, although this would also be nice. Maybe I should explain my current setup better. Firstly, I have a Xen DomU machine running several Dom0's. As each Dom0 is very similar, I started off with a Base install, then created snapshots to modify to create each Dom0. This had the advantage of allowing me to set up a new Dom0 very easily, while taking less physical disk space (and also the side effect that it runs quicker, think that's something to do with the block device cache being used for the origin, but I'm no expert so it may not...) What I would like to be able to do is: (a) be able to take a snapshot of one of these snapshots in order to make backups, or have a bookmark in time if I am doing something I am not sure of (in this instance a 'revert to snapshot' would be nice too) (b) if I need to restore a backup, it would be nice to just be able to dd the image I took as backup onto the snapshot device, without it copying on every write, only copying the sectors (or chunks, whatever the allocation unit for the snapshot COW device is) which are different. These would also be useful for the SAN I am putting together. Both of these I can do manually, the first by creating a snapshot using device-mapper, the second by comparing the sector between the current and the backup before writing. Snapshot of a snapshot done this way is very useful but a pain to set up, although I have written a script to do this for me. Restoration of a snapshot this way is painfully slow (although if functionality of this sort either is not going to be implemented or will take a long time I will recode it in C to (hopefully) speed things up, currently I am using a hack together of bash and perl scripts, just to get it done quickly). Regards Karl Date: Fri, 29 Feb 2008 06:39:50 -0800 From: "Dan Kegel" <dank@kegel.com> Subject: Re: Snapshot of a Snapshot To: "LVM general discussion and development" <linux-lvm@redhat.com> Message-ID: <a71bd89a0802290639t34ee72e7q4379df51e392b900@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 On Fri, Feb 29, 2008 at 3:27 AM, Karl Wagner <kwagner@zetex.com> wrote: > I was just wondering if there was a plan to add 'Snapshot of a Snapshot' > functionality to LVM2? If so, is there any timescale on it? > > This would be a very useful feature, especially in a Xen environment. > > Also, is there an easy way to backup and restore a snapshot? My scenario > is that I am running several Xen DomU's (Virtual machines, 4 of them to > be precise) from snapshots of a base image. However, if one dies (eg the > snapshot overflows, something which should not happen again but just in > case...) and I recreate the snapshot and restore the backup image I > took, it fills the snapshot up. It sounds like you could use a 'revert to snapshot' feature. Is that right? - Dan _________________________________________________________ Zetex Semiconductors - Solutions for an analog world. http://www.zetex.com http://www.zetex.cn E-MAILS are susceptible to interference. You should not assume that the contents originated from the sender or the Zetex Group or that they have been accurately reproduced from their original form. Zetex accepts no responsibility for information, errors or omissions in this e-mail nor for its use or misuse nor for any act committed or omitted in connection with this communication. If in doubt, please verify the authenticity with the sender. _________________________________________________________ _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
