On 2017-09-11 17:36, Pete wrote:
On 09/11/2017 07:49 PM, Austin S. Hemmelgarn wrote:
Unfortunately, I don't know of any overlay mount implementation that
works correctly and reliably with BTRFS. I know for a fact that
OverlayFS (the upstream in-kernel implementation) does not work, and I
believe that AUFS3 and UnionFS (the third-party options that are used by
most LiveCD's) don't work either. UnionFS-FUSE (a userspace
implementation completely unrelated to UnionFS) might work, but I've
never tested it and it will likely have performance issues because it's
implemented in userspace. As far as I know, whiteout support is the
primary missing piece here, but I may be mistaken.
Diverting away from the original topic, what issues with overlayfs and
btrfs?
As mentioned, I thought whiteout support was missing, but if you're
using it without issue, I might be wrong.
I'm using btrfs to create 'base' operating system containers (btrfs) and
then using overlayfs for a few 'upper' containers for specific
applications, so the upper parts of the overlays contain only the config
and data files and I can apply OS updates only on the lower ones.
I do note that changes in the 'base' os can take time to propagate to
the upper containers and I'm probably not being sensible in not stopping
the upper containers when updating the lower ones. This is also does
not seem to be what overlaysfs is intended for. However, for my light
usage it generally works OK and is useful to me.
Actually, this is pretty well in-line with one of the intended use cases
(it was mostly designed for efficient multiple instantiation of Docker
or LXC containers). The other big use case is 'live' systems that only
retain state while powered on, like most install images.
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