Suppose we need to install very big port like llvm80 (about 800MB) as dependency for something like samba410 to the system that has no enought space inside /usr/local file system but has plenty of free space at another UFS file system, so we create symlink /usr/local/llvm80 -> /data/llvm80 before installing. Also, we define WRKDIRPREFIX pointing to /data/tmp.
The port builds and stages just fine but installation fails:
===> Registering installation for llvm80-8.0.1_3 as automatic
pkg-static: Fail to create hardlink: /usr/local/llvm80/bin/.pkgtemp.FileCheck.S4KfobBEtZNB:Cross-device link
*** Error code 70
make: stopped in /usr/ports/devel/llvm80
*** Error code 1
It should not fail.