When you open and close data sets, consider the following guidelines:

• Two or more tasks or two or more DCBs can share data sets on DASD. See Sharing Non-VSAM Data Sets and Sharing PDSEs for more information.
• The system can override volume disposition specified in the OPEN or CLOSE macro if necessary. However, you need not be concerned; the system automatically requests the mounting and demounting of volumes, depending on the availability of devices at a particular time. For more information about volume disposition see z/OS MVS JCL User's Guide.