PREFER, TOOLS, Specify a preferred path for DSA disks.
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        The PREFER command specifies a preferred path for
     DSA disks. This includes RA-series disks and disks
     accessed through the MSCP server. If a preferred path
     is specified for a disk, the MSCP disk class drivers
     (DUDRIVER and DSDRIVER) use the path as their first
     attempt to locate the disk and bring it on line as a
     result of a DCL command MOUNT or failover of an already
     mounted disk. In addition, you can initiate failover 
     of a mounted disk in order to force the disk to the
     preferred path, or to use load-balancing information 
     for disks accessed through MSCP servers.