On Wed, Nov 16, 2016 at 02:32:46PM -0500, Daniel J Walsh wrote:
We would like to change the docker container storage to default to
Overlayfs2 in Fedora 26. But we have a problem on Atomic Host and
Fedora Server distributions.
Currently docker-storage-setup defaults to devicemapper and is hard
coded to setup a thinpool of 40% of remaining disk. Otherwise it sets
up loopback devices on the root file system. Devicemapper is nice
since it works with thinpools and can automatically expand the storage
if the disk space is getting used up.
Moving to Overlay, we can more easily use the root file system directly,
which would be fine for Fedora Workstation. We want to preserve the use
of the remaining storage for Overlay on AH and Fedora Server, since
this would give a user flexibility to switch back to using devicemapper
if they had problems with the Overlay driver.
And being able to do so basically involves following.
- docker-storage-setup creates a logical volume from free space
- Creates a filesystem on that logical volume
- Mounts that logical volume on the directory which docker is going to
use.
mount /dev/docker-vg/foo /var/lib/docker/
- Now when docker users overlay2 graph driver, all the images, containers
and associated metadata will be stored outside the root filesystem and
onto /dev/docker-vg/foo logical volume.
We can not as easily
support the expanding disk for Overlay since we will not use using thinpool.
We have looked at options to hard code OverlayFS with the defaults,
If we always mount /var/lib/docker on on /dev/vg/foo for overlay2 driver
this will be a regression w.r.t current behavior. So I would not
recommend changing current behavior. I think this should be an opt-in.
We are working on provide a config knob to elect this behavior and
atomic host and fedora server will have to opt-in somehow.
I think it will be easy for atomic host as they already drop something
in /etc/sysconfig/docker-storage-setup. Not sure how fedora server
variant will do it.
Thanks
Vivek
> or
> we could just drop a /etc/sysconfig/docker-storage-setup that specified
> Overlay and the percentage of remaining space to use for the
> /var/lib/docker device. But what is the best way to set different
> defaults for AH, Fedora Server and Fedora Workstation.
>
> We would like to discuss with you guys about what you would think is
> the best way to handle.