Can confirm that this BlockingIOError happens on GPFS (alpine) on Summit supercomputer, tested with Python 3.8 and 3.10a7.

I found that it happens only for file sizes above 65536. Minimal example:

This filesize works:

$ rm -f srcfile dstfile && truncate --size 65535 srcfile && python3.10 -c "import shutil; shutil.copyfile(b'srcfile', b'dstfile')"

This file size (and larger) does not work:

$ rm -f srcfile dstfile && truncate --size 65536 srcfile && python3.10 -c "import shutil; shutil.copyfile(b'srcfile', b'dstfile')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/.../usr/lib/python3.10/shutil.py", line 265, in copyfile
    _fastcopy_sendfile(fsrc, fdst)
  File "/.../usr/lib/python3.10/shutil.py", line 162, in _fastcopy_sendfile
    raise err
  File "/.../usr/lib/python3.10/shutil.py", line 142, in _fastcopy_sendfile
    sent = os.sendfile(outfd, infd, offset, blocksize)
BlockingIOError: [Errno 11] Resource temporarily unavailable: b'srcfile' -> b'dstfile'

I tried patching shutil.py to retry the the call on this EAGAIN, but subsequent attempts fail with EAGAIN again indefinitely.

I also use OP's workaround: set _USE_CP_SENDFILE = False in shutil.py