OA47608: >255 EXTENTS POSSIBLE ON EXTENT CONSTRAINT REMOVAL = NO

APAR status

• Closed as Permanent restriction.

Error description

• It is possible to have more than 255 extents on a VSAM cluster
  where Extent Constraint Removal (ECR) is not turned on.  ECR is
  enabled in the SMS data class and allows a VSAM cluster to
  exceed the 255 physical extent limit imposed on regular VSAM
  clusters.  This is possible if Space Constraint Relief (SCR) is
  set to 0% in the dataclass.  When SCR is 0%, it allows DADSM to
  satisfy a space request in more than 5 physical extents.  End of
  Volume code which approximates whether an extend will exceed
  the 255 max limit of extents only accounts for a maximum of 5
  physical extents being returned by DADSM which is not true in
  the case of SCR=0%
  
  Typically this will result in warning messages once the cluster
  exceeds 255.
    IEC161I 254(004)-026
  
  However, the data set will still be processable.  Other
  applications such as DB2 which imply their own limits will
  encounter errors.
  
    DSNP031I DSNPXTN0 - CURRENT SPACE HAS 0284 EXTENTS
        FOR DB2.DSNDBC.CLUSTER
        THE MAXIMUM EXTENTS IS  251.
  
  
  
  CATKEYS: VSAM2015 VSAMEOV VSAMSMS VSAMDB2
  

Local fix

• Activate Extent Constraint Removal in the dataclass to allow for
  >255 physical extents.  Alternatively you can defrag your
  storage group to reduce physical extents or remove Space
  Constraint Removal specification, but this may fail extends.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: ALL VSAM USERS WITH SYSTEM MANAGED VSAM DATA *
  *                 SETS DEFINED WITH DATA CLASS ATTRIBUTES      *
  *                 'EXTENT CONSTRAINT REMOVAL' SET TO N, OR     *
  *                 DISABLED AND 'SPACE CONSTRAINT RELIEF' SET   *
  *                 TO Y, OR ENABLED.                            *
  ****************************************************************
  * PROBLEM DESCRIPTION: A SYSTEM MANAGED VSAM CLUSTER IS        *
  *                      DEFINED USING A DATACLASS WITH 'EXTENT  *
  *                      CONSTRAINT REMOVAL, DISABLED. THE       *
  *                      CLUSTER GROWS IN SIZE AND EVENTUALLY    *
  *                      EXCEEXDS 255 EXTENTS.                   *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  A SYSTEM MANAGED VSAM CLUSTER IS DEFINED IN A DATA CLASS WITH
  THE EXTENT CONSTRAINT REMOVAL  ATTRIBUTE DISABLED OR SET TO N. A
  LIMIT OF 5 EXTENTS CAN BE USED TO SATISFY A PRIMARY OR SECONDARY
  SPACE REQUEST. A TOTAL LIMIT OF 255 EXTENTS CAN BE ALLOCATED TO
  THE CLUSTER. WHEN THE SPACE CONSTRAINT RELIEF ATTRIBUTE IS
  ENABLED OR SET TO Y IN THE SAME DATA CLASS, MORE THAN 5 EXTENTS
  CAN BE USED TO SATISFY A PRIMARY OR SECONDARY SPACE REQUEST. THE
  LIMIT OF 255 TOTAL EXTENTS MAY ALSO BE EXCEEDED.
  

Problem conclusion

• VSAM IS WORKING AS DESIGNED. WHEN SPACE CONSTRAINT RELIEF IS
  ENABLED MORE THAN 5 EXTENTS MAY BE USED TO SATISFY REQUESTS FOR
  PRIMARY AND SECONDARY SPACE ALLOCATION AND THE 255 TOTAL EXTENT
  LIMIT MAY BE EXCEEDED FOR SYSTEM MANAGED VSAM CLUSTERS.
  THE "Z/OS DFSMSDFP STORAGE ADMINISTRATION" MANUAL WILL BE
  UPDATED.  IN THE TOPIC 'DEFINING DATA CLASSES', SUBTOPIC
  DEFINING DATA CLASS ATTRIBUTES', SUBTOPIC 'SPECIFYING ATTRIBUTES
  TO HANDLE SPACE CONSTRAINTS DURING ALLOCATION', A BULLETED ITEM
  WILL BE ADDED TO THE LIST OF ITEMS LISTED AS:
  WHEN YOU REQUEST SPACE CONSTRAINT RELIEF IN ONE OR MORE DATA
  CLASSES YOU MIGHT NOTICE ANY OF THE FOLLOWING:
  - EXTENT CONSTRAINT REMOVAL IS NOT ENABLED BUT VSAM CLUSTERS
  EXCEED THE TOTAL 255 EXTENT LIMIT.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  DFSMS VSAM

• Fixed component ID

  5695DF106

Applicable component levels