Not commenting on the underlying problem, but on your workaround.
On 07-Aug-2015 11:22 pm, "Kragen Javier Sitaker" <kragen@canonical.org> wrote:
>
> Apparently I can’t make /gnu/store a symlink:
[ . . . ]
> I’m working around that by directly mounting the /gnustore partition
> under /gnu/store now.
[ . . . ]
> /tb/gnustore.ext4 /gnu/store ext4 loop 2 3
You don't need to make a new file system and a loop mount. You could just make a bind mount.