On 11/16/2016 02:56 PM, Vivek Goyal wrote: > On Wed, Nov 16, 2016 at 02:49:25PM -0500, Stephen Gallagher wrote: >> 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. > > Ok, that sounds good. We are working on providing a knob to opt-in new > behavior. I think all you have to drop in config file will be something > like. > > /etc/sysconfig/docker-storage-setup > > STORAGE_DRIVER=overlay2 > YET_TO_BE_NAMED_OPTION=VAL > > So upstream default will continue to be devicemapper. We will have to > modify fedora workstation, fedora server and atomic host infrastructure > to opt-in for overlay2. >
Why exactly does this need to be opt-in? Why wouldn't we just change the default on Fedora Server to use overlay2 instead of devicemapper? I think I'm missing some key part of the problem here.
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