# Dataset Space

The Dataset Space attributes provide information about the space allocation and usage for a data set.

Block Size: The physical record size for storage of data in a data set and transfer of that data during an I/O operation. For a DASD data set, block size is maintained in the data set control block (DSCB).

Because more data is being transferred, large block sizes result in higher connect time. Larger blocks with fewer buffers might be appropriate for sequential data sets. Consider using DASD cache control units for heavily used, read-only sequential data sets.

Random access files need smaller block sizes with a larger number of index buffers (when indexed). For PDS libraries, block sizes should usually reflect average number size.

Dataset Name: The 44-character MVS™ name of this data set.

Dataset Type: The data set organization type for this data set. Values are as follows:

- Direct_Access
- Direct_Access_Unmovable
- Extended_Seq_Unmovable
- Extended_Sequential
- Hierarchical_File
- ISAM
- ISAM_Unmovable
- Partitioned
- Partitioned_Unmovable
- PDS_Extended
- Physical_Seq_Unmovable
- Physical_Sequential
- VSAM
- VSAM_Unmovable
- Unknown

Date Created: The date that the current DASD space for this data set was first allocated.

Date Referenced: The most recent date when this data set was opened.

Expiration Date: A date stamp kept on the DASD device where this data set is allocated that indicates when this data set is no longer required. This date stamp is written when the data set is first allocated. Attempting to delete the data set before this date results in a message to the MVS system operator.

Extended Address Space Eligible: Data set is eligible to use Extended Address Space on an Extended Address Volume.

Logical Record Length: The DCB parameter that specifies the length, in bytes, of each record in the data set (fixed format), or the maximum record length (variable or undefined format).

Managed System: The SMS name of this system. An internal node name used to identify the system from which this row of data was obtained.

Number of Extents: The number of separate areas of DASD space allocated to this data set.

Record Format: The DCB parameter that specifies the type and blocking characteristics of records in the data set. These values are:

- F Fixed Length Records
- FB Fixed Length Blocked Records
- V Variable Length Records
- VB Variable Length Blocked Records
- U Undefined Length Records
- D ISCII/ASCII Variable Length Records

See the IBM® publication "MVS DFP 3.3 Using Data Sets" for more information on this and other DCB parameters.

Record Secondary Allocation Unit: The allocation unit for secondary space requests.

Record Secondary Allocation: The amount of space allocated to this data set in secondary allocations.

Secondary Allocation Quantity: The number of space units which are allocated for each data set extent beyond the primary allocation.

Secondary Allocation Unit: The unit in which space is allocated for each data set extent beyond the primary allocation.

Tracks Allocated: The number of tracks reserved for the use of this data set.

Tracks Used Percent: The ratio of tracks used divided by the number of tracks allocated. The value is obtained by dividing the value of the Tracks Used attribute by the value of the Tracks Allocated attribute.

Tracks Used: The number of tracks that actually contain data for this data set.

Unused Tracks: The number of tracks allocated to the data set that are not being used. For VSAM data sets, this is the number of tracks that are not being used at the current high RBA.

Using Cylinder Managed Space: Data set is using Cylinder Managed Space on an Extended Address Volume.

Volume Count: The number of DASD volumes used to contain this data set.

Volume Extents: The count of extents for this data set on this volume.

Volume Sequence: The sequence number of the volume in a multi-volume data set.

Volume: The six-character name assigned to this DASD volume associated with this row of data.

VSAM Key Displacement: The distance in bytes of the key from the beginning of the data record. See the IBM publication "MVS DFP 3.3 Using Data Sets" for more information on this parameter.

VSAM Key Length: The DCB parameter that specifies the length in bytes (0 - 255) of a record key. See the IBM publication "MVS DFP 3.3 Using Data Sets" for more information on this and other DCB parameters.