### Please describe the problem.

I'm using a special directory remote for one of my annex repository. This directory is slow (because it's a FUSE-mounted directory), so I decided to symlink /SPECIALREMOTEDIRECTORY/tmp/ to another drive (as tmp/ is just used during the copy operations). However it doesn't work as expected as git-annex seems unable to copy anything from /SPECIALREMOTEDIRECTORY/tmp/ to /SPECIALREMOTEDIRECTORY/.

    git annex copy --to special_dir myfile
    copy mlyfile (to special_dir...) 
    100%  288 MiB          26 MiB/s 0s         
      /SPECIALREMOTEDIRECTORY/annex/k/tmp/GPGHMACSHA1--800acc67c0803274ed67cea51a1f0df75c225621/: renamePath:rename: unsupported operation (Cross-device link)
    git-annex: copy: 1 failed

    ls -l /SPECIALREMOTEDIRECTORY/annex/k/
    drwx------  1 TroisSinges  wheel  167 22 nov 17:49 fe5
    drwx------  1 TroisSinges  wheel  167 22 nov 17:53 ff5
    lrwx------  1 TroisSinges  wheel   18 23 nov 08:04 tmp -> /Users/TroisSinges/tmp


### What version of git-annex are you using? On what operating system?
git-annex version: 7.20181105 (via Homebrew)
MacOS High Sierra 10.13.6

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
Of course! git-annex is totally amazing in order to manage big collections of files. I'm using it for my videos, and for my photos as well (thousands of files), on Linux and MacOS. Thank you very much for this awesome tool!

