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FASTCPK Technical Detail

The Need For Compaktion

Modern disk arrays are still regarded by the z/OS operating system as a set of conventional DASD volumes. Each logical volume in the array has a fixed number of cylinders, and space is managed in the usual way – with a standard VTOC and VTOCIX. As such, the reasons for re-organizing a DASD volume are, for most z/OS installations, as valid today as they have always been...

Free Space Fragmentation  
  FASTCPK solution

Many disk volumes have small non-contiguous areas of free space spread haphazardly throughout the volume. Although the primary allocation of a new data set can be satisfied in multiple extents, if no single free space extent is large enough, this may force the data set to be allocated from two or more non-contiguous free areas.   FASTCPK can quickly consolidate free space on a volume into as few as one or two contiguous areas.


Multiple Extents  
  FASTCPK solution

Either through natural growth or inaccurate space estimates, data sets often grow beyond their original allocated size. They may end up occupying up to 123 extents and it may become impossible to extend the data set even though a large amount of free space is still available on the volume. This leads to the creation of multi-volume data sets, which have their own special set of requirements (e.g. on backup and restore).   FASTCPK can merge the extents of Sequential, PDS, PDSE, VSAM, DB2 and Extended Format VSAM data sets.


Wasted Space  
  FASTCPK solution

Some data sets on a volume may occupy a larger data space than necessary. This can be caused by inaccurate space estimates or a reduction of the amount of data in the data set. The unused space within these data sets is not available for allocation to other data sets.   FASTCPK can release all or part of the unused space within Sequential, PDS, PDSE, VSAM, DB2 and extended Format VSAM data sets.


VTOC errors  
  FASTCPK solution

Hardware and software system failures can lead to inaccurate VTOCs, which do not reflect the true status of the volume on which they reside.   FASTCPK can analyze a VTOC to detect (and in most cases fix) logical errors, such as invalid F5 DSCBs and incorrect free space definitions.


FASTCPK – Example

The example below illustrates the use of FASTCPK to do a Space Release and Compaktion across all online DASD volumes with volsers beginning “TSO” and “TEST”.
  • The first step releases free space from all inactive PS, PO, and VSAM data sets.

  • The second step does a FASTCPK on any volume where there are more than 20 free space areas. Any active datasets at the time of the Compaktion will not be moved.

  • Although the release and compaktion tasks can be done in a single step, the 2-step technique shown below is faster because the FASTCPK step will move fewer tracks than the single-step job.
//RLSE       EXEC PGM=FDRCPK,REGION=0M
//SYSPRINT    DD  SYSOUT=*
//SYSMAP      DD  SYSOUT=*
//SYSIN       DD  *

    COMPAKT TYPE=RLSE,VOL=(TSO*,TEST*),
    PSRLSE=ALL,PORLSE=ALL,VSRLSE=ALL,NOSECOND=NORLSE

/*

//FASTCPK    EXEC PGM=FDRCPK,REGION=0M,COND=EVEN
//SYSPRINT    DD  SYSOUT=*
//SYSMAP      DD  SYSOUT=*
//SYSIN       DD  *

    COMPAKT TYPE=FASTCPK,VOL=(TSO*,TEST*),
    CPKFREEX=20,LOG=YES,UNABLE=IGNORE

/*


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