Using the NEWCKPTn data sets

In both error and non-error situations, the NEWCKPTn data set specifications can be used during the checkpoint reconfiguration dialog to replace the CKPTn specifications. For example, if an error occurs on CKPT1, JES2 forwards the CKPT1 specification to the NEWCKPT1 specification to replace the unavailable CKPT1 data set. (If the NEWCKPT1 data set has not been pre-defined, or has already been used, the operator can dynamically define it during the dialog. See Replacement data set (NEWCKPTn) definition for further information.)

Forwarding is the process of replacing the CKPTn data set name and volume serial or structure name (if defined on a Coupling facility) with the specifications of its NEWCKPTn counterpart (NEWCKPT1 for CKPT1 and NEWCKPT2 for CKPT2), and the copying of the in-storage version of the checkpoint data to this newly defined CKPTn data set. The NEWCKPTn data set specification then becomes null.

The operator forwards the CKPTn specifications by selecting the appropriate option to the $HASP271 CHECKPOINT RECONFIGURATION OPTIONS and $HASP272 ENTER RESPONSE message pair. (See $HASP271 in z/OS JES2 Messages for these options and an explanation of each.) When the forwarding process is complete, the other members will automatically begin using this newly defined CKPTn data set.

For an example of the forwarding process, see Figure 1 which uses the following checkpoint data set definition:

Note that this example applies equally to checkpoints residing on a Coupling facility structure, except that the STRname= subparameter replaces the DSN= and the VOL= specifications in the following examples.

A Your configuration is running in DUAL mode (that is MODE=DUAL) and your initialization data set has defined a backup data set for both primary data sets. These are specified as SYS1.REPLACE1 and SYS1.REPLACE2 both on volume CHECK3.

    CKPTDEF    CKPT1=(DSN=SYS1.JESCKPT1,VOL=CHECK1),
               CKPT2=(DSN=SYS1.JESCKPT2,VOL=CHECK2),
            NEWCKPT1=(DSN=SYS1.REPLACE1,VOL=CHECK3),
            NEWCKPT2=(DSN=SYS1.REPLACE2,VOL=CHECK3)

B Assume an I/O error occurs to the CHECK2 volume while reading the CKPT2 data set. Data set SYS1.JESCKPT2 on volume CHECK2 becomes unavailable. Effectively, it no longer exists.

C You can forward CKPT2 from the unavailable data set whose name is SYS1.JESCKPT2 on volume CHECK2 to SYS1.REPLACE2 on volume CHECK3 because you have previously defined NEWCKPT2 in your initialization data set. Remember, although you have not altered your initialization data set (it remains as shown in the example) you have altered the data set specifications to the following:

    CKPT1=   (DSN=SYS1.JESCKPT1,VOL=CHECK1)
    CKPT2=   (DSN=SYS1.REPLACE2,VOL=CHECK3)
    NEWCKPT1=(DSN=SYS1.REPLACE1,VOL=CHECK3)
    NEWCKPT2=(DSN=,VOL=)

Note: Following a JES2 restart, the checkpoint data set definitions, as defined in your initialization data set, are read. If the checkpoint data sets have been forwarded, and you have not updated your initialization data set to reflect the new data set definitions, JES2 will use the definitions to provide a pointer to the new data set definitions. However, If you have updated your initialization data set to reflect the new data set definitions, JES2 will use these definitions without doing any forwarding.

Figure 1. Example of checkpoint data set forwarding

Note that CKPT2 is now provided with a new data set name and volume specification (the specification provided by forwarding it to the NEWCKPT2 specification). The NEWCKPT2 specification is now null.