SDF stands for Shared DASD Facility.  It's what keeps track of which
systems and which userids have write access to which minidisks.
SDF records are written on cylinder 0, head 2.
The flags are keyed on starting cylinder address of the minidisk.
To get more information, see DMKSDF ASSEMBLE after a GET CP.
 
There's a CMS command to manipulate and query these flags.
First ATTACH the volume to yourself via LINKVOL.
 
The formats of the CMS command SDF are as follows;
1)  SDF  ?       To get an online explanation of this command.
 
2)  SDF  FORMAT  cuu  volid    To rewrite all the SDF records.
 
3)  SDF  DISPLAY cuu    To display the current settings of the SDF
                        flags.  CPU-1 through CPU-8 correspond to
                               SJEVM1 through SJEVM9 (excluding VM5).
 
4)  SDF  RESET   nodeid cuu|ALL    To reset the SDF flags for this
                                   system only.
                           09/04/89  RC=887 upon completion is ok???