Restrictions for using VSO DEDB areas

VSO DEDB areas have a number of restrictions to their use.

The restrictions include:

• VSO DEDB areas must be registered with DBRC.
• For local VSO DEDB areas, z/OS® data spaces impose a 2 GB (2␠147␠483␠648 bytes) maximum size limit, even though the maximum size of a single or multiple area data set on DASD is 4 GB. If the local VSO DEDB area is more than 2 GB, the area fails to open.

  When Local VSO DEDB areas are opened for preloading, IMS checks to make sure that the area can fit into the data space. If the area cannot fit, the open fails.

  The actual size available in a z/OS data space for a local VSO DEDB area is the maximum size (2 GB) minus amounts used by z/OS (from 0 to 4 KB) and IMS Fast Path (approximately 100 KB).

  To see the size, usage, and other statistics for a VSO DEDB area, enter the /DISPLAY FPV command.

• For shared VSO DEDB areas, z/OS coupling facility cache structures do not place a limit on the maximum size of an area data set. The maximum size of a coupling facility cache structure is 2 GB. If a shared VSO DEDB area is larger than 2 GB, IMS loads a maximum of 2 GB of CIs into the coupling facility cache structure.

  IMS does not check to see if a shared VSO DEDB area can fit into a coupling facility cache structure, regardless of whether the shared VSO DEDB area is preloaded or loaded only when requested.

• The DEDB Area Data Set Compare utility (DBFUMMH0) does not support VSO DEDB areas.