[Yum-devel] snapshots for rollbacks

[seth vidal]

On Sat, 2008-01-19 at 15:20 -0500, Konstantin Ryabitsev wrote:
> On Jan 19, 2008 1:09 PM, seth vidal <skvidal at fedoraproject.org> wrote:
> > > Does the yum plugin live elsewhere? I can only see an apt over debian
> > > (over opensolaris) solution there.
> >
> > I never received the yum plugin. I was told about it from a user inside
> > a very large corporation. The principle of it is fairly simple. Simply
> > have the plugin in the pretransaction state perform a lvm snapshot and
> > save it.
> 
> I may be confused, but I thought LVM snapshots didn't quite work that
> way. You can take a snapshot of a partition and mount it separately,
> for example in order to acquire a consistent backup. With LVM2 you can
> mount snapshots rw, so you can test things out, but it's always done
> on a non-live "backup" partition, and any changes will be thrown away.
> 
> Theoretically, you can do:
> 
> 1. Create a rw LVM snapshot of / and mount it on /mnt/snapshot
> 2. Apply yum updates in the /mnt/snapshot chroot
> 3. Reboot with the snapshot partition as / to test things out (or
> bring up a VM on that root)
> 4. If all is well, reboot back to live partition, destroy the
> snapshot, and apply updates to live
> 5. If all is not well, then just reboot back to live, and destroy all
> attempts at trying
> 
> From reading the linked article, I believe they are talking about the
> features of ZFS, not LVM. If I'm wrong and completely misunderstand
> how LVM snapshots work, then I'll be more than happy to admit it, as
> I'd love to be able to do FS rollbacks like that.
> 

You're not wrong, I was just describing what someone had told me they
had done with a yum plugin and it was highly similar to the apt+zfs
article. sorry for the confusion.

LVM is not unique to the linux implementation. Several lvm mechanisms
(on things like veritas for example) allow snap file system copies.

Again, sorry for the confusion.

-sv