Excerpts from mail: 29-Sep-97 Re: Problems with union mou.. by Brian C.
Grayson@ece.ute 
>   Since your concern is in mounting versions of the source tree,
> you could use OBJDIR stuff, and thus make your source tree
> read-only, right?  If so, mount_union allows NFS mounts.
> In other words, mount_union doesn't enforce the check for whiteout
> support if the upper layer is mounted readonly.  Would that do
> the trick?

    I was able to union mount both the upper and lower layer provided
they are done read-only.  The lower layer can be RO, it's only ever
touched by sup on the remote host.  Ideally I'd like the top layer to be
writable so that I can make my modifications without having to go to the
other machine or even to a different mountpoint.  I assume there is no
such way?

    Is there any way to get NetBSD to "re-export", so that I could just
nfs mount the sparc's union-mounted /usr/src?  It seems that having the
upper and lower layer on NFS will add a lot of traffic that I could get
rid of if I could only just mount the remote mountpoint.  Though from
some tests I've done, the i386 still compiles blazingly fast even when
the source and destination are on NFS.

    Forgive me for not understanding this, but what is whiteout support,
and why doesn't NFS provide it?

    Thanks.

                                                          Will Ferry

-----------------------------------------------------------------------
 William O Ferry  <woferry@CMU.EDU> | finger: woferry@Warp.RES.CMU.EDU
 http://light.res.cmu.edu/~woferry/ | talk:   finger for online status
-----------------------------------------------------------------------