diff -r 001895c39fea Doc/library/ftplib.rst
--- a/Doc/library/ftplib.rst	Wed Jun 11 03:54:30 2014 +0200
+++ b/Doc/library/ftplib.rst	Wed Jun 11 14:26:51 2014 +0200
@@ -266,11 +266,14 @@
 
    Store a file in binary transfer mode.  *cmd* should be an appropriate
    ``STOR`` command: ``"STOR filename"``. *file* is a :term:`file object`
-   (opened in binary mode) which is read until EOF using its :meth:`~io.IOBase.read`
-   method in blocks of size *blocksize* to provide the data to be stored.
-   The *blocksize* argument defaults to 8192.  *callback* is an optional single
-   parameter callable that is called on each block of data after it is sent.
-   *rest* means the same thing as in the :meth:`transfercmd` method.
+   (opened in binary mode) which is read until EOF. *blocksize* tells how many
+   bytes to read from the file on each iteration. *callback* is an optional
+   single parameter callable that is called on each block of data after it is
+   sent. *rest* means the same thing as in the :meth:`transfercmd` method.
+   If :func:`os.sendfile` is available and *callback* is not specified this
+   method will use high-performance :func:`os.sendfile` function to send the
+   file in which case *blocksize* will be ignored.
+
 
    .. versionchanged:: 3.2
       *rest* parameter added.
diff -r 001895c39fea Lib/ftplib.py
--- a/Lib/ftplib.py	Wed Jun 11 03:54:30 2014 +0200
+++ b/Lib/ftplib.py	Wed Jun 11 14:26:51 2014 +0200
@@ -501,15 +501,19 @@
         """
         self.voidcmd('TYPE I')
         with self.transfercmd(cmd, rest) as conn:
-            while 1:
-                buf = fp.read(blocksize)
-                if not buf:
-                    break
-                conn.sendall(buf)
-                if callback:
-                    callback(buf)
+            using_ssl = _SSLSocket is not None and isinstance(conn, _SSLSocket)
+            if callback or using_ssl:
+                while 1:
+                    buf = fp.read(blocksize)
+                    if not buf:
+                        break
+                    conn.sendall(buf)
+                    if callback:
+                        callback(buf)
+            else:
+                conn.sendfile(fp)
             # shutdown ssl layer
-            if _SSLSocket is not None and isinstance(conn, _SSLSocket):
+            if using_ssl:
                 conn.unwrap()
         return self.voidresp()