Full_Description

   By default, Sort/Merge does not allocate contiguous disk blocks
   for the output file. You can request, however, that the output
   file be stored in contiguous disk blocks by specifying the
   /CONTIGUOUS qualifier, thereby decreasing access time. If you use
   the /CONTIGUOUS qualifier, you must also specify the /ALLOCATION
   qualifier because if the preallocated space is too small, OpenVMS
   RMS may be unable to extend the file contiguously.