VSAM data set characteristics

Some information in the following field definitions is taken from VSAM Demystified (SG24-6105-01). For more information about this publication, see the related links.

VSAM type: Choose the type of VSAM data set to allocate:

KSDS: Key-sequenced data set. A VSAM data set whose records are loaded by ascending key sequence and controlled by an index. Records are retrieved and stored by keyed access or addressed access and new records are inserted in key sequence because of free space allocated within the data set. Relative byte addresses of records can change because of control interval or control area splits.

ESDS: Entry-sequenced data set. A data set whose records are loaded without regard to their contents and whose relative byte addresses cannot change. New records are added at the end of the data set.

RRDS: Relative record data set. A type of VSAM data set containing fixed length records which are accessed by relative record number.

Catalog ID: Identifies the integrated catalog facility (ICF) catalog that contains the entry for this data set. The default is the system catalog search order.

VSAM associations: Providing a name for the data component and index component of a VSAM data set allows you to process the data portion separately from the index portion.

Data: Identifies the data component of the data set. The data component is the part of a VSAM data set, alternate index, or catalog that contains the data records. If the data name is not specified, it is generated.

Index: Identifies the index component of the data set. Using the index, VSAM is able to randomly retrieve a record from the data component when a request is made for a record with a certain key. If the index name is not specified, it is generated.

Key length: The length of the key field within each data record. Specify a value from 1 to 255. This field is used by VSAM to build the index. The sum of the key length and key offset cannot exceed the length of the shortest record.

Key offset: The position of the key within the record. Specify a value from 0 to the length of the shortest record. The sum of the key length and key offset cannot exceed the length of the shortest record.

CI size: The size of the control interval for the data component of the data set. A control interval is a fixed-length area in which VSAM stores records. It is the unit of transfer between VSAM and disk storage.

Buffer space: The minimum buffer space to be allocated at open time.

Share cross region: Specify how the cluster can be shared among users on one system:

1: The cluster can be shared by any number of users for read processing or accessed by only one user for read and write processing.

2: The cluster can be shared by any number of users for read processing and accessed by one user for write processing.

3: The cluster can be fully shared by any number of users.

4: The cluster can be fully shared by any number of users, and buffers used for direct processing are refreshed for each request.

Reuse: Specify YES or NO to indicate whether the data set can be reset to empty status at open time.

Recovery: Specify YES or NO to indicate whether the storage allocated to your data component is to be formatted before records are inserted.

Spanned: Specify YES or NO to indicate whether to allow a data record to span control intervals.

Erase: Specify YES or NO to indicate whether the space occupied by the data set is to be overwritten with binary zeros when the data set is deleted. Leave this field blank to use the erase option set when the entry was defined or last altered.

Writecheck: Specify YES or NO to indicate whether the catalog is to be checked by a direct access device operation called write check when a record is written.

Space units: Defines the unit of primary and secondary space to be allocated. The default value is TRK. Select one of the following values:

REC: A record of average size.

KB: A kilobyte (1024 bytes).

MB: A megabyte (1048576 bytes).

TRK: a track of a direct access storage device (DASD).

CYL: A cylinder of a DASD.

Primary units: The amount of DASD space to be used for primary space allocation. The range depends on the Space unit specified and the type of DASD. The default value is 10.

Secondary units: The amount of DASD space to be used for secondary space allocation. The range depends on the Space unit specified and the type of DASD. The default value is 10.

Average recsize: For RRDS, the length of all records in the data set or, for other data set types, the average length of records in the data set.

Maximum recsize: The maximum length of the data records.

Freespace percent CI: The percentage of each control interval that is to be set aside as free space when the VSAM data set is initially loaded, during a mass insert, and after a CI-split.

Freespace percent CA: The percentage of each control area that is to be set aside as free space when the VSAM data set is initially loaded, during a mass insert, and after a CI-split.

Volume serial or serials: Specify a volume on which a cluster's components are to have space.

CI size: The size of the control interval for the index component of the cluster.

SMS definitions: Storage Management Subsystem is an operating environment that helps to automate and centralize the management of storage. SMS provides a storage administrator with control over data class, storage class, management class, storage group and ACS routine definitions.

Data class: Name of a data class that is defined in your System Managed Storage (SMS) installation. Do not enter a value on a system without SMS.

Storage class: Name of a storage class that is defined in your System Managed Storage (SMS) installation. Do not enter a value on a system without SMS.

Management class: Name of a management class that is defined in your System Managed Storage (SMS) installation. Do not enter a value on a system without SMS.