Thursday, March 12, 2015

Difference between PDS and PDSE - Brief discussion

We all know that a PDS (partioned data set), commonly referred to as Library in Z/OS world is a collection of several data sets which we call as members. A PDS internally contains a directory which keeps track of the member names.
A PDS is created with a Data Set Organization of PO , (DSORG=PO), which stands for partitioned organization.

Creating PDS using 3.2 option
Directory blocks  . . 20
Data set name type  : PDS
Using JCL:

However a PDS have certain disadvantages:
1. When we delete a member from a PDS, the space remains unused. We need to compress the PDS using 'Z' at the command line , or we can use IBM utility  IEBCOPY to reclaim the unused space.

2. Also as we know, a PDS internally contains a directory. As the size of the PDS grows, ie, as we add more and more members into the pds, the directory size gets near to the threshold (This Directory size we give when we define a PDS), after which we can not add any more members in the PDS.
Then we need to copy all the members into a new PDS with increased Directory size.

PDSE ( partitioned data set extended ):  Exactly same as PDS in many respects.
However , PDSE  data sets can be  stored only on DASD, not on tape. Interesting thing is the directory can expand automatically  as needed. Additionally it has an index which helps to locate the members inside the PDSE faster . SPACE from deleted members are automatically reused in PDSE .

JCL to create PDS
//SYSIN    DD    *
    ALLOC -
    NEW -
    STORCLAS(RM06) -
    MGMTCLAS(RM06) -

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