Fix read/write behavior and return value depending on direct_io

Also add parallel direct write option for 6.2+ kernels.

src/fs_copydata_readwrite.cpp

@@ -65,11 +65,9 @@ namespace l
     size_t  totalwritten;
     vector<char> buf;
 
-    bufsize = (128 * 1024);
+    bufsize = (1024 * 1024);
     buf.resize(bufsize);
 
-    fs::lseek(src_fd_,0,SEEK_SET);
-
     totalwritten = 0;
     while(totalwritten < count_)
       {