Generation and Version of GDG - and confusion?

[Prakash Jha]

Hi,

I got confuse about generation and version -- what is the difference between Generation and Version of GDG. When does generation number increments? And when does version number increment - are they both necessary?

[Robert Sample]

A.B.C.G0001V00 references GDG base A.B.C and generation 1. Version 0 is normal and typical. The ONLY way to create version 01 is to write to A.B.C.G0001V01 -- if you do so, the system will uncatalog A.B.C.G0001V00 and catalog A.B.C.G0001V01 in its place. A GDG allows you to define up to 255 generations in the catalog. Specifying A.B.C(+1) indicates to the system that you are going to create the next generation; A.B.C(0) means you are referencing the most recently created generation. Specifying A.B.C (with no relative generation) indicates to the system that you want all generations, starting with the most recent and working back to the oldest.

When a GDG adds a generation, and there are already the limit in the catalog, the OLDEST generation "rolls off" the GDG and will no longer be cataloged. Depending upon the way the GDG is set up, that generation may be deleted from disk / tape when rolled off.

Generation and version are both necessary -- generations will increment any time (+1) is specified but versions must be manually incremented by GxxxxVyy in the JCL.

[Prakash Jha]

Thanks Robert. This is great explanation, appreciate your help...