/sys$common/syshlp/helplib.hlb
DEFRAGMENT, FILE, Qualifiers, /RVN
 *Conan The Librarian 

       /RVN=n
       /RVN=0 (default)

          When you have a bound volume set, use this qualifier
          to identify a disk from the volume set or all disks
          in the volume set. The default of zero tells the Disk
          File Optimizer to defragment all disks in the bound
          volume set. Specify a relative volume number (RVN)
          to defragment a specific disk that belongs to a bound
          volume set.
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