You can share data in address spaces and data spaces. You can use any storage to which you have valid access, except for 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 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.
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.