You can share data in address spaces and data spaces. You can use any storage to which you have valid access, except for a subspace, a hiperspace, a VIO window, a V=R region, the PSA or the nucleus (read-only, extended read-only, read-write and extended read-write areas). The target area cannot contain page-protected or page-fixed pages. Storage that is currently allocated through DIV MAP to any DIV object cannot be the target, nor can the source storage have been allocated through DIV MAP to a hiperspace.
Authorized programs can use an unlimited number of pages for sharing. However, use care to ensure that it is used appropriately. System performance can be affected if programs use large amounts of storage for many source areas, but having many targets of one large or a few small sources can reduce central storage constraints.
ESQA storage requirements increase as more storage is shared. The formula for the number of bytes of ESQA storage used by the systems is: 40 bytes per shared page group plus 40 bytes per shared page view. For example, a single shared page group with two views requires 40+40*2 = 120 bytes of ESQA storage.
The maximum number of shared pages for a program in problem state with PSW key 8-15 is 32, unless this number is modified by your installation. This number includes both the source and targets, so the actual number of unique pages is 16. Your installation can use the IEFUSI installation exit to change the limit for problem state programs. See z/OS MVS Installation Exits for details on IEFUSI.
In order to expedite the return of all internal control blocks for the shared storage back to the system, IBM® recommends issuing IARVSERV UNSHARE against all views for both source and target that are originally shared. For an example of how to code the UNSHARE parameter, see z/OS MVS Programming: Assembler Services Reference IAR-XCT.