On Thu, 2 Dec 2010, Amir Goldstein wrote: > On Thu, Dec 2, 2010 at 10:23 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote: > > On Wed, 1 Dec 2010, Amir Goldstein wrote: > > > >> On Wed, Dec 1, 2010 at 7:41 PM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote: > >> > > >> > QCOW2 format supports other neat features like compression, encryption and > >> > snapshots. None of those feature are supported in this patch and the question > >> > is, do we need it ? I can imagine for example snapshots to be useful for > >> > roll-back changes made by e2fsck, but this is hardly problem of e2image itself. > >> > > >> > So, please look at the patch, try it and let me know what else you thing is > >> > useful to implement, or what would you like to change. > >> > > >> > >> Hi Lukas, > >> > >> This is very cool :-) > >> My wish is to export next3/ext4 snapshots as qcow2 snapshots. > >> I actually thought of implementing e2image -x <snapid> as a way to > >> export a snapshot image, > >> but using qcow2, file system can be exported with all of it's snapshots. > >> It should be quite trivial since next3 snapshots contain a map of changed blocks > >> and I suppose qcow2 snapshots should be the same. > >> Now I only need to find the time to do it... > >> > >> Amir. > > > > Hi Amir, > > > > I seems like a cool feature, so when QCOW2 infrastructure is in place > > adding snapshots to it should not be a big deal (not that QCOW2 > > infrastructure is :)), however I was wondering are you planning to > > export only metadata, or even data itself ? > > > > There are 2 applications I can think of for exporting snapshots. > One needs only the metadata and the other requires the data as well. > > 1. Rollback to snapshot (metadata only) > ---------------------------------------------------------- > Unlike ZFS/Btrfs, there is no inherent way to "rollback to snapshot" > with Ext4 snapshots. > Instead, all changed metadata needs to be copied over from snapshot. > The only plausible way to do this is to un-mount the file system (or > re-mount read-only), So, you're saying that it would not be possible to implement in-kernel snapshot roll-back for ext4 with snapshots ? I find this hard to believe, because we can always freeze the filesystem a do whatever we want to do, or am I missing something ? If it would be possible this would be much better solution then exporting and restoring it from QCOW2 image. > use e2image to export a metadata image of a snapshot to a different > location and then > overwrite the filesystem with snapshot metadata (data blocks are > already in-place). > > This method can be applied today, even without qcow2 support, but with > qcow2 snapshots, > you can generate a single e2image, which can be used to rollback to > any snapshot and to > restore the original filesystem (as long as the rolled back version > wasn't modifed). > > 2. Filesystem replication (data + metadata) > -------------------------------------------------------------- > This application is inspired by ZFS replication: > http://wikitech-static.wikimedia.org/articles/z/f/s/Zfs_replication.html > The idea is to start with a remote replica by transferring a full copy > of snapshot N1 > and then push incremental differences N1..N2 to roll the replica to snapshot N2. > So if e2image has the ability to export a full snapshot image (including data) > and the capability to export incremental qcow2 snapshots, those could > be transferred > to the remote location and be used to create and update the replicated > filesystem. I am sorry but I do not really get it, can't you just export filesystem data + metadata into qcow2 image without any qcow2 snapshot functionality and then recreate the whole filesystem from this image ? It seems to me that you do not need qcow2 snapshot functionality to do this, however I might be missing something. > > So to answer your original question ("what else you thing is useful to > implement"), > e2image -d would be nice (export data blocks). This is really easy thing to do, so I can do this :). Thanks! -Lukas > > Amir. > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
