Generation data group support

Generation data groups (GDGs) enable you to store multiple data sets, called generation data sets (GDSs), as versions of the GDG. You cannot use FTP to create a new GDG, but you can use it to create a new version (that is, a new GDS) or to transfer an existing version of an existing GDG.

The relationship between DCBDSN and GDGs is governed by MVS™ allocation rules rather than FTP usage rules. Therefore, when creating a new GDG [put ‘sys1.proclib(jes2)’ user77.mygdg(+1)], at least one of the following must be true:

A valid MODEL or PATTERN DSCB (for FTP, DCBDSN) specification must be coded in the FTP.DATA file when the z/OS® FTP server is started.
A valid SITE DCbdsn=dataset_name must be issued before a PUT command is issued.
A data set having the same name as the GDG base must reside on the volume as the user catalog that contains the GDG definition. In this case, neither a SITE DCbdsn or a DCBDSN argument in the FTP.DATA data file is required. Allocation detects that a GDG is being created and looks in the VTOC of the volume containing the USERCATALOG for a data set (uncataloged) that has the same name as the GDG BASE (see the sample GDG JCL that follows).
Notes:
1. A model or pattern DSCB that is the same name as the GDG BASE cannot exist on an SMS managed volume. This is an SMS restriction and is documented in the DFP manuals pertaining to using data sets (generation data sets or generation data groups).
2. Allocation does not generally have any requirements about the characteristics of a MODEL DSCB (cannot be VSAM, must be on DASD). Most facilities create one model DSCB for the entire system and everyone uses that model. The system-wide model usually has no logical record length (LRecl), block size (BLKsize), record format (RECfm), data set organization (DSORG) or retention period (RETpd) associated with it.
3. The z/OS FTP server requires the MODEL DSCB to have a valid DSORG of physical sequential organization (PS). Otherwise the SITE command for the DCBDSN is ignored, and a message is issued indicating the DCBDSN was ignored.
4. GDGs are MVS-specific structures. Other operating systems might not support this structure. Using FTP to send GDG members to other operating systems is not guaranteed to yield the same results as an MVS-to-MVS transfer.
5. The REName subcommand does not guarantee serialization of the GDG data set. Use the PUt subcommand instead. See Informational APAR II08285 for more information.

The following restrictions apply:

DCBDSN=USER.MYGDG(0)/ USER.MYGDG(-n), not supported
DCBDSN=SYS1.PROCLIB(JES2), specifying a member of a PDS is not valid
DCBDSN=SYS1.PROCLIB, valid
The data set referenced on the DCBDSN, a DSORG of PS needed (FTP requirement)

Note: If explicit values are associated with LRECl, BLKSIZE, RECFM, or the SMS management equivalent parameters, these explicit parameters override the values associated with the model DSCB specified on the DCBDSN. The MVSGet and MVSPut subcommands configure LRECL, BLKSIZE and RECFM values which override the values that are associated with the model DSCB.

The following is a sample Job Control Language (JCL) to create a model and the GDG BASE:

USER77.MYGDG         -MODEL/PATTERN
VOL=SER=CPDLB1       -Volume having USERCATALOG, where USER77 is defined
(NAME(USER77.MYGDG)  -GDG BASE definition
 
//USER77X  JOB MSGLEVEL=(1,1),MSGCLASS=D,NOTIFY=USER77
//GDGA EXEC PGM=IDCAMS
//*
//GDGMOD   DD DSN=USER77.MYGDG,
//        VOL=SER=CPDLB1,
//            UNIT=SYSALLDA,
//            SPACE=(TRK,(0)),
//            DCB=(LRECL=80,RECFM=FB,BLKSIZE=6800,DSORG=PS),
//            DISP=(,KEEP)
//SYSPRINT DD SYSOUT=*
//SYSIN    DD *
  DEFINE GENERATIONDATAGROUP -
         (NAME(USER77.MYGDG) -
         EMPTY -
         NOSCRATCH -
         LIMIT(255) )