Best Practices for Allocating Dump Space

The following are best practices regarding dump space allocation:
  • Use the DUMP option on the CP_OWNED system configuration file statement to reserve certain spool volumes to be used for dump space only. Also, fully allocate these DUMP volumes as SPOL space. These practices reduce spooling space fragmentation and will enable dump space allocation to find large clusters of available space.
  • You should allocate space for more than one dump. Space for three dumps is recommended -- space for the next dump and space for two dumps that you may not have yet processed with the CP DUMPLOAD or DUMPLD2 utilities. It is recommended you purge dumps from spool after loading them to disk and successfully transmitting them to IBM® Support, or when you are sure they are no longer needed.

Additional Hints and Tips

  • When assigning devices for dump space, remember to consider that the speed of the device directly influences dump time.
  • The following CP commands can be used to query and/or modify dump space:
    • The QUERY DUMP command provides information regarding the amount of spool (dump) space required for a dump of the system, given the status of the system at the time of the query. This command tells you how many pages are reserved on each spool volume. Note that a dump can span multiple spool volumes.
    • A privilege class B user can display the current dump setting with the QUERY DUMP command. A privilege class D user can display the current spool space status with the QUERY ALLOC SPOOL command. A privilege class D user can determine if any dump SPOOL files (spool class D) exist by issuing CP QUERY RDR ALL CLASS D SHORTDATE.
    • A class B user can change the dump setting with the SET DUMP command. The SET DUMP command also allows the class B user to specify a preferred order of multiple disk volumes to be used for allocation of the dump space.
    • The SNAPDUMP and SET DUMP commands allow you to optionally include the CP frame table and user PGMBKs in a dump. Your calculations for dump size should assume these values are included when calculating the amount of dump space needed.

    For more information on these CP commands, see z/VM: CP Commands and Utilities Reference.