Data Set Compatibility Considerations

CMS can read and update VSAM data sets created under VSE/VSAM or OS/VS. VSAM data sets with physical record sizes .5K, 1K, 2K, or 4K created under CMS can be read and updated by OS/VS VSAM. See the VSE/VSAM General Information Manual for more information about VSE/VSAM and OS/VS VSAM.

If you perform allocation on a minidisk in CMS, you cannot use that minidisk in an OS virtual machine in any manner that causes further allocation. VSE/VSAM (and thus CMS) ignores the format-5, free space DSCB on VSAM disks when it allocates extents. If allocation later occurs in an OS machine, OS attempts to create an accurate format-5 DSCB. However, the format-5 DSCB created by OS does not correctly reflect the free space on the minidisk because OS expects it to be a full pack. In CMS, allocation occurs whenever data spaces or data sets are defined, and space is released whenever data spaces, catalogs, and data sets are erased.