VOLSEL parameter for SMSSELCT

A VOLSEL parameter must be assigned.

However, VOLSEL=SRM should not be used with SMSSELCT. This option specifies DFSMS should select the volume and will effectively disable SMSSELCT processing in the rule.

Related topic

SMSSELCT—control selection of volumes from SMS storage groups

Volumes are selected from the storage group that is assigned to the SMS-managed data set. The VOLSEL rule list parameter specifies the method of volume selection to be performed (BESTFIT, CRITDSN, DPO, HISTDPO, MAXSPACE, or PERCENT), allowing significant control over volume selection within the pool.

During volume selection, DFSMS passes available volumes in the defined storage pool or pools to DADSM (Direct Access Device Space Management) processing to complete the allocation. It is not uncommon for DFSMS to make multiple calls to DADSM to satisfy an allocation under one or more of the following circumstances:

  • The requested space is not very small
  • The storage pool or pools are experiencing a lot of activity
  • The storage pool or pools are becoming full

Important

Documentation on IBM's DFSMS volume selection can be found in the conventional volume selection section of z/OS DFSMSdfp Storage Administration.

The SMSSELCT function with a VOLSEL option of BESTFIT, MAXSPACE, or PERCENT can improve your allocation performance by selecting the best volume to satisfy the requested space for DFSMS. This effectively limits the number of calls to DADSM to just one.

VOLSEL options are described as follows:

  • BESTFIT selects the volume with the smallest contiguous extent that satisfies the primary allocation.

    For allocations on extended address volumes (EAVs), the available extents on the entire volume will be used for data sets that are eligible to use Extended-Addressing Space (EAS); for all other data sets, the allocation will use the available extents in the Base-Addressing Space (BAS).

  • CRITDSN controls allocations by specifying data sets that should not reside on the same volume.

    Warning

    CRITDSN is resource intensive and should be used only for a small list of critical data sets. It should not be used without considering the system impact.

  • DPO specifies volume selection based on performance statistics accumulated by BMC AMI Storage.

  • HISTDPO specifies volume selection based on historical volume performance.

    Important

    HISTDPO requires more resources than normal allocations.

  • MAXSPACE specifies that the volume with the largest single contiguous extent should be selected.

    For allocations on extended address volumes (EAVs), the available extents on the entire volume will be used for data sets that are eligible to use Extended-Addressing Space (EAS); for all other data sets, the allocation will use the available extents in the Base-Addressing Space (BAS).

  • PERCENT specifies that the volume with the largest percentage of free space should be selected.

    For allocations on extended address volumes (EAVs), the available extents on the entire volume will be used for data sets that are eligible to use Extended-Addressing Space (EAS); for all other data sets, the allocation will use the available extents in the Base-Addressing Space (BAS).



 

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