On 11/16/2016 02:40 PM, Vivek Goyal wrote: > 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. > Today, Fedora Server relies on whatever is the default for docker-storage-setup. We just tell Anaconda to reserve up to 15GiB by default for the / partition and then it puts all remaining free space (on drives selected to be used by Anaconda) into a single logical volume with no partitions. It's a very easy thing for us to drop a different config file for docker-storage-setup into place for Server. So if that's all we need to do, let me know and I'll work it up.
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