VFS Union mounts suck for Live CDs

Tim Gardner tim.gardner at canonical.com
Tue Jul 14 13:44:32 BST 2009

I believe it is the consensus among those folks testing VFS union mounts
that its not a workable alternative for Live CDs compared to AUFS in
Jaunty. Therefore Andy Whitcroft has prepared a commit series to the
Karmic kernel tree that will add AUFS back to our builds.

Following is an edited transcript of our discussion.

On Sun, Jul 12, 2009 at 08:14:35PM -0600, Tim Gardner wrote:
> As for aufs, I thought it was kind of a long shot from the beginning
>> that we'd be able to avoid using it. Looks like I'm gonna have to 
>> cave on this one, huh?

It was a useful exercise.  A lot of good has come out of it.  For one we
now have a fuse based fallback for next cycle meaning we can have live
cds from alpha-1 regardless of the state of the kernel support.  We have
forged good links and gained upstream karma from helping out in testing
and driving the implementation fo VFS union mounts.  I am hopeful we
will have something upstream for LL even if we do have to have aufs in
here for one more cycle.  Plus although aufs is a bit of a mess, it is a
whole heap less of a mess as a result of you pushing hard to get the
maintainer to push it upstream.  That meant that slurping it up seems to
be a much easier exercise than one might have expected and the result is
more reliable than we have seen in the past (as more people are paying
him to maintain it).

But yes, I think we are reaching the point where we have to say, VFS
union mounts are not going to make 2.6.31 and therefore not going to
make Karmic.  If so then my personal opinion is that aufs2, while being
a suboptimal external module, it is at least better than it has been in
the Intrepid and Jaunty releases, and is a devil we know and foundations
have installer support for.

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