Layering is a concept generally associated with data that is striped. A layer in a striped environment is defined as the relationship of the volumes that make up the total number of stripes. That is, those volumes that will participate as part of the I/O packet. Once any volume or volumes, up to a maximum of stripe count, composing this I/O packet changes, this constitutes another layer. As relates to striped data, the volumes that constitute this I/O packet should be viewed in the same context as a single volume data set, as opposed to multivolume if the data were not striped. Once the data set extends to a second layer, this would be analogous to a multivolume nonstriped data set. Again, the definition of striped is a stripe count greater than 1. The sequential access method (SAM) does not support the concept of multi-layering. VSAM supports multi-layering. Figure 1 shows an example of the concept of layering with a four-stripe data set.