The extent of data set sharing within one operating system depends on the data set disposition and the cross-region share option specified when you define the data set. Independent job steps or subtasks in an MVS system or multiple systems with global resource serialization (GRS) can access a VSAM data set simultaneously. For more information about GRS see z/OS MVS Planning: Global Resource Serialization. To share a data set, each user must specify DISP=SHR in the data set's DD statement.