Currently, when a generation data set is dynamically allocated using keyword GDG(Y), the GDG base must be previously defined.  With BQQ3841, functionality has been added to create the GDG base if it does not already exist.

The following is an example using the GDG(Y) keyword with the MODEL statement:

GLBL DBRC(Y) DSALLOC(Y) ICALLOC(Y) DBALLOC(Y)     
MODEL NAME(IC1) RETPD(015) UNIT(CARTVTS) GDG(Y) + 
      DSN(RCU.BRI15.IC4.&DBD.&DSGACT)             
OIC DBD(C8HOXP) DDN(C8DD1) IC((*,IC1))            
OIC DBD(C8HOXP) DDN(C8DD2) IC((*,IC1))            
OIC DBD(C8HOXP) DDN(C8DD3) IC((*,IC1))            
OIC DBD(C8HOXP) DDN(C8DD4) IC((*,IC1))            

Example messages showing the GDG was created if necessary.

BMC8300I C8HOXP,C8DD1A GDG ALLOCATED, NAME=RCU.BRI15.IC4.C8HOXP.C8DD1A
BMC8300I C8HOXP,C8DD2A GDG ALLOCATED, NAME=RCU.BRI15.IC4.C8HOXP.C8DD2A 
BMC8300I C8HOXP,C8DD3A GDG ALLOCATED, NAME=RCU.BRI15.IC4.C8HOXP.C8DD3A 
BMC8300I C8HOXP,C8DD4A GDG ALLOCATED, NAME=RCU.BRI15.IC4.C8HOXP.C8DD4A 

Below are some additional keywords that control the allocation of the GDG:

EXTENDED Keyword
 
Use the EXTENDED keyword to specify if the GDG is to be in extended format or not.  Extended format GDGs can contain up to 999 Generation Data Sets(GDSes) while non-extended format GDGs can contain up to 255 GDSes.
The Extended format GDG is supported in Z/OS V2R2 and later and must be enabled in the system.  
 
Uses
Optional in predefined models and on MODEL control statements.
 
Related
MODEL, EMPTY, EXTENDED, GDG, SCRATCH.
 
Syntax
EXTENDED(value).
Value
      Y – Generate extended format GDG base.
      N – Generate non-extended format GDG base.
 
Default
     EXTENDED(N)
 
EMPTY Keyword
 
Use the EMPTY keyword to specify what action is to be taken for the catalog entries of the GDG when the number of generation data sets in the GDG is equal to the LIMIT value and a new generation data set is to be cataloged. The final disposition of the actual data sets uncatalogued from the GDG base is determined by the setting of the SCRATCH/NOSCRATCH parameter for the GDG base.
 
Uses
Optional on the MODEL control statement.
 
Related
MODEL, EMPTY, EXTENDED, GDG, SCRATCH
 
Syntax
EMPTY(value)
 
Value
      Y – Remove all GDS entries from the GDG when a new Generation data set is created that causes the LIMIT value to be exceeded     
      N – Remove only the oldest Generation Data set entry when the LIMIT value is exceeded.
 
Default
     EMPTY(N)
 
LIMIT Keyword
 
Use the LIMIT keyword to specify the maximum number of generation data sets to be associated with the GDG to be created.                       
Uses
Optional in predefined models and on MODEL control statements.
 
Related
MODEL, EMPTY, EXTENDED, GDG, SCRATCH
 
Syntax
LIMIT(value)
 
Value
      The value is dependent on whether the GDG base is defined as EXTENDED or not.
       If EXTENDED=Y, the value can be from 1 to 999.
       If EXTENDED=N, the value can be from 1 to 255.
 
Default
     255 or 999 depending on the GDG base is non-extended or extended.  
 
 
SCRATCH Keyword
 
Use the SCRATCH keyword to specify what action is to be taken for a generation data set located on DASD when the data set is uncatalogued from the GDG base due to EMPTY/NOEMPTY processing. The parameter is ignored for generation data sets located on tape.
 
Uses
Optional on the MODEL control statement.
 
 
Related
MODEL, EMPTY, EXTENDED, GDG, LIMIT
 
Syntax
SCRATCH(value)
 
Value
      Y – Delete the generation data set from disks when uncatalogued from the GDG base.
      N – Do not delete the data set when it is uncatalogued from the GDG base. If the data set is SMS-managed, it is re-cataloged as a non-VSAM data set but is not associated with the GDG base any more. 
Default
     SCRATCH(Y)