Libvirt Snapshot Question

[Elias Mobery]

Hey Peter, thanks for the super quick reply, you're awesome!

So you mean the first option would be to create a second disk instead of
using snapshot for write, when it gets too big I can then unplug the disk,
delete it (or wipe entire overlay fs) and recreate it to start fresh?

OK I will try that, thanks for the tip!

Option 2 with trim/discard I have to do some research, this seems a bit
more challenging.

Thank you SO much for the great advice. I will try everything out and
report back. :-)


On Tue, Nov 30, 2021, 3:25 PM Peter Krempa <pkrempa at redhat.com> wrote:

> On Tue, Nov 30, 2021 at 14:51:54 +0100, Elias Mobery wrote:
> > Hello Peter, thank you so much for that detailed info!
> >
> > Sorry, you were right, when trying to delete my external snapshot via
> > snapshot-delete, the error says "deletion of external snapshots
> unsupported"
> >
> > I can't merge the snapshot because the VM image is in a read-only
> > filesystem. Sorry I should've said, it's a live system. So the image is
> in
> > the read-only squashfs and external snapshot in overlay is used for
> writing.
>
> Okay, that changes the situation quite a bit:
>
> >
> > Now I would like the snapshot emptied or deleted/recreated when it
> reaches
> > 4GB.
> >
> > Is there even a way to do this with the image being read-only?
>
> If the base image is on a read-only filesystem you obviously can't
> commit to it.
>
> Now the question is what should happen to the data in the overlay.
>
> Discarding/recreating the overlay image is possible only once you turn
> off the VM because it basically rolls back the state of the disk back to
> the time when the overlay was created. This means that everything
> written to the disk will be lost.
>
> Filesystems obviously can't handle that so that's why it simply won't be
> possible to do live with the root image.
>
> You can have a second disk, which you hot-unplug, wipe the overlay and
> plug it back.
>
> Another possibility is to enable trim/discard and just simply delete the
> data in the VM which was added after the overlay was created. When
> trim/discard is enabled on all layers incluging the guest filesystem,
> then deleting stuff inside the VM will also mean that the overlay will
> shrink again.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20211130/d664e11e/attachment.htm>