The maximum size of a VSAM data set is 4 GB (4␠294␠967␠295 bytes) unless it is defined with a data class that specifies a DSNTYPE of EXT (extended format) with the extended addressability (also in the data class) set to Y (yes). A VSAM data set can be expanded to 123 extents per volume. In addition to the limit of 123 extents per volume, these are the other limits on the number of extents for a VSAM data set:

• If non-SMS-managed, then up to 255 extents per component.
• If SMS-managed, then the following are true:
  • If not striped and without the extent constraint removal parameter in the data class, then up to 255 extents per component.
  • If striped and without the extent constraint removal parameter in the data class, then up to 255 extents per stripe.
  • If the extent contraint removal parameter in the data class is set to a value of Y, then the number of extents is limited by the number of volumes for the data set.