Update hca/dss/util/__init__.py

Co-Authored-By: Hannes Schmidt <hannes@ucsc.edu>

Author: chmreid

hca/dss/util/__init__.py

@@ -58,9 +58,10 @@ def hardlink(source, link_name):
         if source_stat.st_dev != dest_stat.st_dev or source_stat.st_ino != dest_stat.st_ino:
             raise
     except OSError as e:
-        # ELINK can occur when max number of links has been reached
-        # EPERM can occur when writing to NFS
-        copy_on_error = (errno.EMLINK, errno.EPERM)
+        copy_on_error = (
+            errno.EMLINK,  # max. number of hard links exceeded
+            errno.EPERM,  # observed on NFS mounts (issue #519)
+        )
         if e.errno in copy_on_error:
             # FIXME: Copying is not space efficient; see https://github.com/HumanCellAtlas/dcp-cli/issues/453
             log.warning('Failed to link source `%s` to destination `%s`; reverting to copying', source, link_name)