Please describe the problem.

Ref: Original issue and finding report against datalad.

What version of git-annex are you using? On what operating system?

Windows 8.20200815-g335aae266 (I see now that I might benefit from update, but I found no related issue so likely it is something new)

Please provide any additional information below.

{920}[Level 5] CommandError: '"git" "annex" "add" "-c" "annex.dotfiles=true" "-c" "annex.retry=3" "--json" "--json-error-messages" "--debug" "--" "file.dat"' failed with exitcode 1 under C:\Users\DataLad\AppData\Local\Temp\datalad_temp_tree_q4wxn05d [out: '{"command":"add","success":false,"error-messages":["  file.dat failed to link to annex"],"file":"file.dat"}'] [err: '[2020-10-15 11:57:07.4657537] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.dotfiles=true","-c","annex.retry=3","show-ref","git-annex"]
| [2020-10-15 11:57:07.4813787] process done ExitSuccess
| [2020-10-15 11:57:07.4813787] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.dotfiles=true","-c","annex.retry=3","show-ref","--hash","refs/heads/git-annex"]
...
| [2020-10-15 11:57:07.6376287] call: cp ["--reflink=auto","-a","file.dat",".git\\annex\\objects\\6f0\\fbd\\SHA256E-s7--ed7002b439e9ac845f22357d822bac1444730fbdb6016d3ec9432297b9ec9f73.dat\\SHA256E-s7--ed7002b439e9ac845f22357d822bac1444730fbdb6016d3ec9432297b9ec9f73.dat"]
| "cp": unrecognized option `--reflink=auto'
| Try `"cp" --help' for more information.
| [2020-10-15 11:57:07.6532537] process done ExitFailure 1

C:\tmp>cp --help | grep ref
  -d                           same as --no-dereference --preserve=link
  -L, --dereference            always follow symbolic links
  -P, --no-dereference         never follow symbolic links

C:\tmp>cp --version
cp (GNU coreutils) 5.97
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Written by Torbjorn Granlund, David MacKenzie, and Jim Meyering.

if I parsed NEWS.gz correctly, that option was added in * Noteworthy changes in release 8.0 (2009-10-06) [beta] . So I wonder if git-annex could sense for version of cp or presence of --reflink option and not use it if cp is too old?

Meanwhile I will see if there is some sensible way to get more uptodate coreutils (or cp) at least within conda env