VSAM Demystified

1.10. Extended addressability

With extended addressability the 4 GB VSAM architectural limit for data set size imposed by using the 4-byte field for the relative byte address (RBA) was eliminated.

It is important to state up-front that extended addressability and extended format are not the same concept. Extended format is a way of storing data in a 3390/3380 logical volume. Extended addressability provides the ability to have larger VSAM data sets. However, extended format is a prerequisite for extended addressability.

Using extended addressability, the size limit for a VSAM data set is determined by either:

• CI size multiplied by 4 GB

• The volume size multiplied by 59

A 4 K CI size yields a maximum data set size of 16 TB, while a 32 KB CI size ...