You use the parmlib member EDGRMMxx VLPOOL command to define pools and to set actions that you want taken on all the volumes that reside in the pool. The VLPOOL MASTEROVERWRITE operand controls how DFSMSrmm allows the overwriting of a volume. You can specify if you want to allow data to be appended to the end of a volume or overwritten, or to allow new files to be added to a volume. The MASTEROVERWRITE value applies to all volumes that reside in a pool. This diagram shows the syntax of the VLPOOL MASTEROVERWRITE operand.

If you do not specify the VLPOOL MASTEROVERWRITE value, DFSMSrmm uses the value that is set with the DFSMSrmm EDGRMMxx OPTION MASTEROVERWRITE operand.

>>-VLPOOL------------------------------------------------------->

>--+---------------------------------------------------------+-><
   |                     .-option_masteroverwrite_value-.    |   
   '-MASTEROVERWRITE--(--+-MATCH------------------------+--)-'   
                         +-USER-------------------------+        
                         +-ADD--------------------------+        
                         '-LAST-------------------------'        

ADD

Specify this value so new data can be created and no existing data can be destroyed. No existing file on a volume can be recreated, but the last file can have new data added to it. When adding data to the last file, DFSMSrmm checks that the data set name used must match the existing data set name. Select this option when you want the last file on the volume to be extended or a new file added to the volume.

Note: DFSMSrmm enforces the MASTEROVERWRITE(ADD) option on a WORM tape that is in master status. This is done to ensure that you see a message from DFSMSrmm rather than one of a number of symptoms as a result of the tape drive preventing overwrites.

LAST

Specify this value to ensure that when an existing file on a master volume is being written to that only the last file on the volume can be used. The data set name used must match the existing data set name. Select this option when you want the last file on the volume to be used for output.

MATCH

Specify this value to ensure that when an existing file on a master volume is being used for output that exactly the same data set name must be used. Select this option when you want any existing file on the volume to be recreated regardless of whether it is the last file on the volume as long as the same data set name is used.

When you use an existing tape file for output all the files which are higher in sequence are destroyed.

USER

Specify this value to allow any existing file on a master volume to be used for output regardless of the data set names being used and its relative file position on the volume. Select this option when you want validation of master volumes to be just the same as for user status volumes.

When you use an existing tape file for output all the files which are higher in sequence are destroyed.

Default: The DFSMSrmm parmlib member EDGRMMxx OPTION command MASTEROVERWRITE operand value when you do not specify a VLPOOL MASTEROVERWRITE value.