CKPTn data set definition and placement on DASD

Checkpoint data sets should reside on a high-speed, low-usage device, and they should be allocated on a cylinder boundary. If available, the best location for each data set is on a dedicated 3390 device. To obtain optimum performance, the CKPT1 and CKPT2 data sets should be the only data sets on their respective DASD volumes if your configuration is operating in DUAL checkpointing mode. If your configuration is operating in DUPLEX mode, the data set defined by the CKPT1= parameter should reside on a separate volume. (See Checkpoint configuration modes for an explanation of DUAL and DUPLEX modes.)

IBM® suggests placing the CKPTn data sets on separate volumes to ease recovery. If the CKPTn data sets are physically removed from one another, they have separate power sources, separate control units, and no single common point of failure.

Note: All members of a MAS configuration must have at least one channel path to the device containing the primary checkpoint data set(s).

Figure 1 provides an example for defining checkpoint data sets.

Figure 1. Example of Defining Checkpoint Data Set

//ALLOCATE JOB  (...),'PREPARE FOR JES2',MSGLEVEL=1
//ALLOCAT  EXEC PGM=IEFBR14
//*
⋮
//*
//CHECK1   DD   DSN=SYS1.JESCKPT1,UNIT=3390,
//              VOLUME=SER=CHECK1,DISP=(NEW,KEEP),
//              SPACE=(ABSTR,(45,15)),DCB=(DSORG=PSU)
//*
//CHECK2   DD   DSN=SYS1.JESCKPT2,UNIT=3390,
//              VOLUME=SER=CHECK2,DISP=(NEW,KEEP),
//              SPACE=(TRK,13256),DCB=(DSORG=PSU)
/*

Performance can be severely degraded if the checkpoint data set(s) resides on a SPOOL volume; avoid placing a checkpoint data set on a SYS1.HASPACE data set.

If you use global resource serialization, it is strongly recommended that you add the checkpoint data set(s) to the member exclusion resource name list (RNL). If you do, global resource serialization does not delay a JES2 member's access to the data sets checkpoint data sets. See z/OS MVS Planning: Global Resource Serialization for further information on this procedure.

Attention: Do not use a hardware RESERVE to serialize access to any other data set on the CKPT1 or CKPT2 volumes. If you do, serious degradation of JES2 throughput or a deadlock situation can result.