General Sharing Considerations

If you can, you should not share volumes among multiple VSE images.

Both data integrity and system performance are always impacted, sometimes in subtle ways.

Many VM/VSE users in the past chose to provide a single pool of workfile space for VSAM and/or SAM workfiles which was shared among all the VSE images. To be sure, the pooling concept saves DASD space, but does impact performance when compared with choosing to implement separate workfile space pools for each VSE image which need not be specified as shared. In the conditions of shared workfile space pools, the VTOCs and catalogs for the shared volumes can readily become very significant bottlenecks impacting batch throughput and critical path time through your batch processing window.

With modern DASD, it may be economical to re-evaluate this choice -- using more "virtual DASD" volumes that do not need to be shared may be a better way, even though additional DASD may be required.

With some care in planning, you can arrange compiles, sorts, and other users of workfile space pools so that they do not normally share data volumes.

Remember that if only one file on a volume needs to be shared, the volume must be shared, even though all the other files on that volume are used by only one VSE image.