The PDSMAN Library Space Reuse facility offers a proactive solution to the problem of PDS out-of-space conditions and the related issues of unscheduled compressions, unnecessary compressions and PDS over-allocation. This facility dynamically reuses the dead PDS space whenever a member is updated. The space occupied by a deleted or replaced member is recorded and is made available for use by this or future updates. PDSMAN records space information in a special member (normally named $$$SPACE) called the Space Map that is created in the library.
IMS expects its MFS library members to have two bytes of binary zero user data in their directory entries. Since the PDSMAN Space Map member does not have user data written in this special format, IMS fails to start properly.