In addition to Bill's comments, make sure the application can support the Data Table.
For a User Maintained Data Table (UMT), the full File Control API commands are not available. For a CICS startup, it opens the UMT VSAM file, reads all the records into a Data Space and then closes it. This file can be taken to other systems that might also want access. This type of approach really suits an ESDS structure that is needed for Read-Only.
For a CICS Maintained Data Table (CMT), all the File Control commands are available, as in Delete, Update and Write. This means that CICS will keep all changes made to the Data Table in sync with the source dataset.
If the CMT is needed by multiple AORs, then consider a Shared Data Table for your CMT, this is much faster than using a File Owning Region and the mirror task.
CICS will allocate the size of the Data Space based on the MAXNUMRECS option in the File Control entry. Be careful if you take the NOLIMIT default option, as it could affect your Paging subsystem.