Following up the mail below, some more "Googling" turned up this patch... http://www.gnome.org/~markmc/code/lvm-snapshot-merging/lvm-patches/lvm-lvmer ge.patch which seems fairly recent (2006-05-10). Has anyone tried it or know anything about it? > -----Original Message----- > From: linux-lvm-bounces@redhat.com [mailto:linux-lvm-bounces@redhat.com] > On Behalf Of Roger Lucas > Sent: 17 August 2006 14:00 > To: 'LVM general discussion and development' > Subject: Merging snapshots - does lvmerge or similar exist > forLinux > > Hi, > > I have seen a few questions about this but could not find any answers. > > I am working with Debian, the 2.16.20 kernel and the latest LVM+DMAPPER > releases. > > I have a logical volume that I want to be able to make changes to, but > unroll these changes again if necessary. When the operations are > finished, > I want to end up with just one LV and no additional snapshots. The LV > would > either have its original contents or the updated contents, and this > decision > isn't made until all the changes have been done. > > With LVM2, the snapshots are r/w so I could either: > > 1) Snapshot the original LV and keep the snapshot safe, then make the > changes to the original LV. If I don't need to restore the LV after > applying the changes, then I can just delete the snapshot. If I do want > to > restore the original LV, however, what is the best way to flush the > changes > in the snapshot back onto the original LV ? > > I appreciate that I could just "dd" the snapshot onto the LV to restore > its > orignal state, but this will rewrite a lot of data that hasn't actually > changed. Apart from being slower than I would like, I don't know if > writing > exactly the same data to the LV will trigger the data to be written to the > snapshot - if it does then the snapshot will grow in size to the original > LV > whilst the "dd" happens, and I do not have enough disk space for that. > > Or > > 2) Snapshot the original LV and make the changes to the snapshot. If I > want > to restore the original LV, then all I need to do is delete the snapshot. > But, if I want to keep the changes (and not have to keep the snapshot), > how > can I flush the changes that have been made to the snapshot back onto the > original LV. > > I appreciate that I could just "dd" the snapshot onto the LV to update it > to > the new values, but I don't like this for the same reasons as in (1) > above. > > Is there an "lvmerge" command or similar on Linux LVM. There appears to > be > one for the HP-UX LVM but I couldn't see one for Linux. > > Alternatively, is the snapshot disk format easy enough to analyse so that > a > lvmerge utility could be written relatively easily ? > > Thanks, > > Roger > > > _______________________________________________ > 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/ _______________________________________________ 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/
