When you have a share that exports a multi-volume filesystem, different parts of the file system have different amounts of free space. Currently Samba does not take this into account and always returns the amount free at the base of the share.
Patch for 4.0.next:
git cherry-pick 233b32b771188a6b9ee730a2a202023370e80746
from master (applies cleanly to 4.0.next).
Created attachment 8537 [details]
git-am version for 3.6.x.
Version for 3.6.next (including char *filename -> const char *filename fix).
Re-assigning to Karolin for inclusion in 4.0.next and 3.6.next.
Pushed to v3-6-test and autobuild-v4-0-test.
Pushed to v4-0-test.
Closing out bug report.