OA51583: DOCUMENTATION FOR SSR FEATURE ADDED IN 2.2 NEEDS TO BE ADDED TO THE DFSMS MANUALS

APAR status

• Closed as documentation error.

Error description

• There is no documentation explaining the new Secondary Space
  Reduction function in z/OS 2.2.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of Space Constraint Relief (SCR).      *
  ****************************************************************
  * PROBLEM DESCRIPTION: There is incomplete documentation for   *
  *                      Secondary Space Constraint Relief in    *
  *                      IBM Publications: DFSMS Using the New   *
  *                      Functions, DFSMSdfp Storage             *
  *                      Adiministration and DFSMS Using         *
  *                      Datasets.                               *
  ****************************************************************
  * RECOMMENDATION: Use Space Constraint Relief as applicable.   *
  ****************************************************************
  There is incomplete documentation for
  Secondary Space Constraint Relief in
  IBM Publications: DFSMS Using the New
  Functions, DFSMSdfp Storage
  Adiministration and DFSMS Using
  Datasets.
  

Problem conclusion

• The IBM Publications below will be updated
  with the following information about Secondary
  Space Reduction:
  
  
  IBM z/OS DFSMSdfp Storage Administration,
  Chapter9. Defining data classes ,
  Specifying attributes to handle space constraints
  SG23-6860-30
  
  You can specify attributes on Page 2 of the Data Class
  Define panel to indicate whether or not to retry new data
  set allocations or extends on new volumes that fail due to
  space constraints. During allocation, there might not be
  enough space on a volume to meet the requested space. SMS
  volume selection can sometimes solve this problem by trying
  all candidate volumes before failing the allocation. You
  can also use the Space Constraint Relief and Reduce Space
  Up to (%) attributes to request that an allocation be
  retried if it fails due to space constraints. SMS retries
  the allocation by combining any of the following:
  
  * Spreading the requested quantity over multiple volumes
  * Allocating a percentage of the requested quantity
  * Using more than 5 extents
  
  Space Constraint Relief
  Specifies whether or not to retry an allocation that was
  unsuccessful due to space constraints on the volume. Before
  it is retried, the allocation is attempted on all candidate
  volumes. Space Constraint Relief applies only to
  system-managed data sets. As of z/OS V2R2 there is
  Secondary Space Reduction (SSR) support, that is,
  Space Constraint Relief applies to both primary and secondary
  allocations.  This feature must be enabled before a retry
  is attempted and is disabled by default. Space Constraint
  Relief is applicable during extend to the current volume
  and for create or extend to a new volume. This parameter is
  only valid for non best-fit allocations
  
  Note: The caller of the allocation request can override the
  Space Constraint Relief parameters in the Data Class. DFSMSdss
  is an example of a product that might do this.DFSMSdss
  enables Space Constraint Relief to remove the 5-extent limit
  without reducing the primary quantity, and in some cases
  requests the best fit methodology.
  
  See the following publications for more information about
  this feature.
  
  'IBM z/OS DFSMS Using Datasets, Section Allocation of Data
  Sets with the Space Constraint Relief Attributes,
  SC23-6855-30'.
  'IBM z/OS V2R2: Storage Management and Utilities, Section
  1.3.2 Space Constraint Relief for Secondary Allocation,
  SG24-8289-00'.
  
  Specify one of the following:
  Y  Specifies that SMS retry the allocation.
  N  Specifies that SMS does not retry the allocation if
     the original amount cannotbe acquired.This is the default.
  
   ===========================================================
  
  
  IBM z/OS DFSMS Using Datasets, Section
  Allocation of Data Sets with the Space Constraint Relief
  Attributes
  SC23-6855-30
  
  To reduce allocation failures, three data class attributes
  can influence the allocation and extension of data sets to
  new and current volumes. Allocations that might have failed
  for lack of space can succeed.
  
  The attributes are:
  Space Constraint Relief (values are YES or NO). This
  specifies whether or not to retry an allocation that was
  unsuccessful due to space constraints on the volume. Space
  Constraint Relief is disabled by default and as of V2R2,
  Space Constraint Relief also applies to secondary space.
  
  Reduce Space Up To % (0 - 99%). Used with Space Constraint
  Relief, this specifies the amount by which you want to
  reduce the requested space quantity when the allocation is
  retried.
  
  Dynamic Volume Count (1 - 59 or blank). This is used during
  allocation processing to determine the maximum number of
  volumes a data set can span. It allows the number of
  primary volumes to increase, if necessary, without adding
  any candidate volumes to the catalog.
  
  Allocations and extends to new volumes proceed normally
  until space cannot be obtained by normal means.
  
  The system performs space constraint relief in two
  situations: when a new data set is allocated and when a
  data set is extended to a new or current volume. During
  CREATE processing, the primary quantity might be reduced
  for both non-VSAM and VSAM data sets.
  
  Space constraint relief, if requested, occurs in one or two
  methods, depending on the volume count that you specified
  for the failing allocation.
  
  1. If the volume count is greater than 1, SMS attempts
    to satisfy the allocation by spreading the requested
    primary allocation over more than one volume, but no more
    than the volume count specified.
  2. If method 1 fails or if the volume count is 1, SMS
     modifies the requested primary space or the secondary space
     for extension, by the percentage that you specified in the
     REDUCE SPACE UP TO parameter.
  
  The allocation fails as before if either or both methods 1
  and 2 are not successful. Two fields can be used to track
  the use of space constraint relief for secondary allocation:
  
  * SMF64SSR: Indicates whether secondary space reduction was
    performed using the attributes specified for Space
    constraint Relief.
  
  * SMF64NTA: Indicates the size of extent that is returned
    in tracks.
  
  See the following publications for more information about
  this feature.
  
  'IBM z/OS V2R2: Storage Management and Utilities, Section
  1.3.2 Space Constraint Relief for Secondary Allocation,
  SG24-8289-00'.
  
  'IBM z/OS DFSMSdfp Storage Administration, Section
  Specifying Attributes to Handle Space Constraints During
  Allocation, SG23-6860-30'.
  Recommendation: You can specify 0% in the data class for
  this parameter so space is not reduced.
  
  ==========================================================
  
  IBM z/OS DFSMS Using the New Functions,
  Chapter15. Using the SMS enhancements,
  SMS Space Constraint Relief
  SC23-6857-30
  
  SMS space constraint relief processing provides relief for
  space-related failures for SMS managed data sets. Space
  Constraint Relief is disabled by default. When space
  constraint relief is requested, SMS retries an allocation
  that was unsuccessful due to space constraints on the
  volumes. Depending on the allocation characteristics, SMS
  may retry with a one-step or two-step process after the
  initial phase failed for insufficient space.
  
  In the one-step process, SMS retries the allocation after
  reducing the requested space quantity based on the Reduce
  Space Up to (%) attribute. SMS simultaneously removes the
  5-extent limit so that SMS can use as many extents as the
  data set allows. The one-step process is used when
  allocating a data set that has a volume count of 1,
  allocating a data set with guaranteed space or extending an
  existing data set to a new volume.
  
  In the two-step process, SMS first uses a best-fit volume
  selection method to spread the primary quantity over
  multiple volumes, up to the volume count, if needed. If
  this fails due to space constraints, SMS continues with the
  best-fit method after reducing the primary quantity and
  removing the 5-extent limit. The two-step process is
  generally used when the volume count is greater than 1.
  
  z/OS V2R2 provides the following enhancements to SMS space
  constraint relief:
  
  * Space Constraint Relief is available on Secondary
    Space as of V2R2 and is also known as Secondary Space
    Reduction (SSR).
  
  * Supports a new parameter in the data class that
    indicates whether space reduction on guaranteed space
    allocation is permitted or not.
  * Supports the space reduction function on
    non-striped guaranteed space allocations when allocating a
    new data set or extending an existing data set to a new
    volume. This space reduction function will remain
    unsupported for striping allocation as the system requires
    all stripes to have the same space quantity.
  * Allocates the largest possible space that satisfies
    the percentage specified in the parameter, Reduce Space Up
    to (%), during space reduction processing for both
    guaranteed space and non-guaranteed space allocation
    requests. If the reduced space is not available on the
    current volume, the secondary extent is allocated on
    another volume. For VSAM each extent must return space in
    multiples of the CA size. If the reduced minimum secondary
    allocation amount falls below the minimum CA size, then the
    minimum CA size is used as the minimum secondary allocation
    amount.
  * Issues a new SMS message to the job log and
    hardcopy log when the Dynamic Volume Count (DVC) function
    is invoked. For more information, refer to the topic
    about Specifying attributes to handle space constraints
    during allocation in z/OS DFSMSdfp Storage Administration.
  
  See the following publications for more information on this
  feature::
  'IBM z/OS V2R2: Storage Management and Utilities, Section
  1.3.2 Space Constraint Relief for Secondary Allocation,
  SG24-8289-00'.
   'IBM z/OS DFSMSdfp Storage Administration, Section
  Specifying Attributes to Handle Space Constraints During
  Allocation, SG23-6860-30'.
  
  'IBM z/OS DFSMS Using Datasets, Section Allocation of Data
  Sets with the Space Constraint Relief Attributes,
  SC23-6855-30'..
  

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