vgoyal added a new comment to an issue you are following:
Flipping from one to the other will take free space somewhere for the
'atomic storage export/import' operation to temporarily store docker images and
A way around the xfs lack of shrink issue is to put the filesystem containing /var onto a
thinly provisioned LV (be it a dir on rootfs or its own volume). After 'atomic storage
reset' wipes the docker storage, issue fstrim, and all the previously used extents
will be returned to the thin pool, which can then be returned to the VG, which can then be
reassigned to a new docker thin pool. Convoluted in my opinion, but doable.
IIUC, you are saying that use a thin LV for rootfs to work around xfs shrink issue? People
have tried that in the past and there have been talks about that many a times. There are
still issues with xfs on top of thin lv and how no space situation is handled etc. Bottom
line, we are not there yet.
So if we can't use rootfs on thin LV and if xfs can't be shrinked, then only way
to flip back to devicemapper is don't allow rootfs to use all free space. And have
free space which can either
be used by overlay2 or devicemapper for container storage.
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