[pkg-go] Bug#1050993: podman: Podman should use overlay storage driver by default instead of vfs

[Gregor Riepl]

Hi Reinhard,

> I've now worked on packaging 4.6.2, and it is currently available
> in debian/experimental. Can you do me a favor? Please test it and let me 
> know whether
> it fixes this issue.

Thanks, it looks very promising!

On a system without any storage.conf files, but with existing vfs 
container storage, podman kept using the vfs driver. Trying to force the 
overlay driver with --storage-driver overlay resulted in an error, as 
expected.

After removing ~.local/share/containers it started using the overlay 
driver automatically. Trying to force vfs resulted in an error, also as 
expected.

I think this is very sensible behavior and a news message may not even 
be required. On the other hand, existing vfs users would miss out on the 
advantages of overlay storage. Since migration is not trivial, it might 
be helpful to include migration instructions.

> I'm happy to add a note in NEWS.Debian, which is going to be presented
> on package upgrades. Can you please provide a wording for that text that you
> would have been useful to you?

How about this?

----
Podman 4.6 changes the default storage driver from vfs to overlay.
The overlay driver has been available for some time, but it had to be 
enabled explicitly in the Debian version of podman. The overlay driver 
is generally much faster and uses less disk space than the vfs driver.
.
To take advantage of overlay, it's necessary to delete local container 
storage. Make sure to save or export any images, containers and volumes 
before doing so, or you will lose them!
.
Some helpful commands:
.
# save the filesystem of a container
podman export -o important-container.tar important_container
# save a volume
podman volume export -o important-volume.tar important_volume
# save all container images
podman save -o images.tar
# delete ~/.local/share/containers
# check that podman is using the overlay driver
podman info | grep graphDriverName
# re-import all container images
podman load -i images.tar
# re-import a saved container filesystem as a container image
podman import important-container.tar
# re-import a volume
podman volume import important_volume important-volume.tar
----

Maybe some web links could be helpful. I haven't found anything complete 
though.