Attributes of automatically created output data sets

For those output data sets that do not already exist at the beginning of the initialization phase of an online reorganization, IMS creates the data sets.

IMS creates the data sets with the following attributes:
Number of Volumes
If a particular input data set is SMS-managed, IMS creates the corresponding output data set with the same number of volumes.

If the input data set is not SMS-managed, IMS automatically creates the corresponding output data set only when the input data set resides on a single volume. For a non-SMS-managed input data set that resides on multiple volumes, you must create the corresponding output data set before starting the online reorganization.

Location of SMS-managed output data sets
If a particular input data set is SMS-managed, the corresponding output data set is also SMS-managed, and uses the same storage class as the input data set.

Your site's storage administrator must ensure that this storage class refers to a storage group with sufficient space to hold the output data set, or that the automatic class selection (ACS) routine selects an appropriate storage class for the data set.

Location of non-SMS-managed, non-VSAM output data sets
Regardless of the type of DASD on which the input data set resides, IMS creates the corresponding non-VSAM output data set using the equivalent of a DD statement UNIT=SYSALLDA parameter.

When it creates the output data set, IMS does not request any specific volume serial number, thus allowing the data set to be created on a storage volume or, if no storage volume is available, on a public volume.

Location of non-SMS-managed, VSAM output data sets
IMS creates a VSAM output data set on the same volume as the corresponding input data set. This restriction can limit the usefulness of automatically creating a VSAM data set that is not SMS-managed.
Format of the output data sets (DSNTYPE)
IMS uses the format type of the input data sets for the output data sets. If the input data sets are defined as OSAM sequential large format data sets (DSNTYPE=LARGE), IMS automatically defines the output data sets as large format data sets.
Size of output data sets on a single volume
When the input data set has extents on only one DASD volume, IMS creates the output data set on a single volume using the equivalent of a DD statement VOLUME=(,,,1) parameter.
The amount of primary space for the output data set is derived from the space allocation of the input data set:
  • For a non-VSAM data set, the primary space is the total amount of space in the first five extents on the volume.
  • For a VSAM data set, the primary space is the primary space allocation used when the input data set was created.

If you specified secondary space amount for the input data set, IMS uses this same secondary amount for the output data set.

To reserve approximately the same amount of space for the output data set as was reserved for the input data set, regardless of the DASD types involved, IMS requests the space for the output data set as a number of OSAM blocks or VSAM records. For input data sets that did not specify a number of OSAM blocks or VSAM records, IMS converts the cylinder or track allocation to an equivalent number of blocks or records.

An automatically created output data set could have a considerably different amount of available DASD space than was used for the input data set. For example, for an input data set that used secondary allocation, the automatic creation process reserves the primary space for the output data set, but there might not be enough space on the volume for secondary allocation either during the online reorganization or during later database processing.

Size of output data sets on multiple volumes (SMS-managed only)
IMS automatically creates multiple-volume output data sets only when the input data set (and, therefore, the output data set) is SMS-managed. You can determine the storage class by examining the input data set or the site's ACS routine.

Although it is not strictly a requirement for SMS-managed multiple-volume output data sets, you should ensure that the storage class specifies the guaranteed-space attribute. By specifying the guaranteed-space attribute, you allow VSAM to use the primary-space allocation for each of the volumes when it creates the output data sets. Secondary space is used as needed. However, even with the guaranteed-space attribute, the output data sets might not have the same amount of space as the input data sets, especially if secondary-space allocation was used for the input data sets.

The requested primary and secondary space is based on the input data set's space allocation on the first DASD volume.

Block or control interval (CI) sizes of output data sets

If you are not altering the structure of a database, each output data set that IMS creates for an online reorganization has the same block or control interval size as its corresponding input data set.

If you are altering the structure of a database by using the ALTER option of the INIT OLREORG command and you specified ALTERSZE values for one or more data set groups in the RECON data set, IMS creates the output data sets for which you specified ALTERSZE values with block or CI sizes that match the ALTERSZE values.

When the ALTER option is used, the online reorganization applies to the entire HALDB database. For each partition that contains block or CI sizes that must change, the ALTERSZE values must be set separately before you issue the INIT OLREORG command.

To set ALTERSZE values prior to a reorganization that alters the structure of a database, you can use either the DBRC command CHANGE.PART.

For VSAM data sets, if you specify an ALTERSZE value and the output data set already exists with a CI size that does not match the ALTERSZE value, the reorganization fails for the partition. If this happens, you must correct the discrepancy between the ALTERSZE value and the CI size and, after alter processing is complete for all other partitions in the database, reissue the INIT OLREORG command with OPTION(ALTER) specified. One way you can correct a discrepancy between an ALTERSZE value and a CI size is to delete the existing VSAM data set so that the alter function can automatically create the data set with the new CI size.

For OSAM data sets, the alter function can change the block sizes even if the output data sets already exist.