From Page 1 of the Data Class Define panel, issue the DOWN command to view Page 2, on which you specify volume and data set attributes.

Data Set Name Type

Specifies the format in which the data set is to be allocated. When you specify extended format, you can also select requirements for the data set, including the need for extended addressability.

See z/OS DFSMS Using Data Sets for detailed information on assigning and allocating data classes for extended format data sets.

The available values are:

EXT

Specifies that the data set to be allocated is in the extended format. All VSAM data set types can be allocated in the extended format (with the exception of key range data sets, temporary data sets and system data sets).

If you specify EXT, you must also specify a value for the If Ext subparameter. The other subparameters are primed with the following defaults: Extended Addressability = No, and Record Access Bias = USER.

Sequential extended format data sets can be version 1 or 2. The user can specify the version number with the second value of DSNTYPE on the DD statement or dynamic allocation equivalent. The PS_EXT_VERSION keyword in the IGDSMSxx member in PARMLIB can change the default for the version number.

If the sequential extended format data set is striped or if it resides only on one volume, then the version number does not matter. If it is not striped and it resides on multiple volumes, then the version number affects whether the system can use FlashCopy. FlashCopy can handle version 2 in that case but not version 1. PTFs are available to allow proper handling on releases earlier than z/OS® 2.1.

HFS

Specifies that the data set is a hierarchical file system (HFS) data set.

LARGE

Specifies that the data set is a large format data set. Large format data sets are physical sequential data sets with the ability to grow beyond the limit of 65 535 tracks per volume.

The BLOCKTOKENSIZE=REQUIRE option in the IGDSMSxx member of SYS1.PARMLIB affects what programs can open these data sets. See the description of the IGDSMSxx member inz/OS MVS Initialization and Tuning Reference.

These data sets cannot be written on a system older than z/OS 1.7. These data sets cannot be read on a system older than z/OS 1.7 if they have more than 65535 tracks on each volume.

LIB

Specifies that the data set is a PDSE.

PDS

Specifies that the data set is a partitioned data set.

blank

Leaves the Data Set Name Type attribute value unspecified. This is like coding DSNTYPE=BASIC on the DD statement but you cannot specify BASIC on this panel.

If you specify a Data Set Name Type of EXT for data sets allocated in extended format, you can specify additional attributes:

If Ext

Specifies whether allocation in extended format is preferred or required. If you specified EXT for the Data Set Name Type attribute, you must also specify one of the following:

P (preferred)

The data set allocation is attempted in nonextended format if the necessary system resources for extended are not available.

R (required)

The data set allocation fails if the data set cannot be allocated in extended format.

Extended Addressability

Specifies that a VSAM data set in the extended format be allocated using extended addressability. This lets the data set grow beyond the four gigabyte (4GB) size. The data set can be a VSAM data set in any record organization but must be allocated in the extended format.

The available values are:

Y

Extended addressability is used.

N

Extended addressability is not used. This is the default.

Record Access Bias

Specifies whether to let VSAM determine how many and which type of buffers to use when accessing VSAM extended format data sets by batch processing. This is known as system-managed buffering, and is available to VSAM data sets in any record organization which are allocated in the extended format.

Tip: The buffering algorithms determined by VSAM can be overridden by using JCL.

The available values are:

System

Specifies that VSAM chooses how many buffers to use and how they are processed.

System-managed buffering only takes effect if the application requests the use of non-shared resources (NSR). It is not effective for applications requesting local shared resources (LSR), global shared resources (GSR), or record-level sharing (RLS).

The number of buffers and the buffering technique are determined by the system or the user:

• The system, based on application specifications (ACB MACRF=(DIR,SEQ,SKP)) and the values for direct and sequential millisecond response (MSR) and bias specified in the storage class.
• The user, as specified on the JCL DD card (AMP=('ACCBIAS=).

If sequential processing is to be used, the system optimizes the number of buffers and uses the NSR buffering technique. If direct processing is to be used, the system optimizes the number of buffers and uses the LSR buffering technique. You can change the defaults for space and the relative amount of hiperspace when direct optimization is used by using the following keywords in the AMP= parameter: SMBVSP=, SMBHWT=, and SMBDFR=.

User

Specifies that system-managed buffering is not used. This is the default.

SO

Specifies that system-managed buffering with sequential optimization is to be used.

SW

Specifies that system-managed buffering weighted for sequential processing is to be used.

DO

Specifies that system-managed buffering with direct optimization is to be used.

DW

Specifies that system-managed buffering weighted for direct optimization is to be used.

RMODE31

RMODE31 allows you to specify whether or not to allocate the buffers and control blocks in 31-bit addressable storage.

The values you may specify for RMODE31 are:

ALL

Control blocks and buffers above the line.

BUFF

Buffers (only) above the line.

CB

Control blocks (only) above the line.

NONE

Control blocks and buffers below the line.

Dynamic Volume Count

Dynamic Volume Count is used during allocation processing to determine the maximum number of volumes a data set can span. The number can be in the range 1 through 59. The default value is 1. 59 is the z/OS volume limit.

During define processing, Dynamic Volume Count allows for a larger number of volumes to be considered without increasing the number of candidate volumes stored in the catalog. During existing data set allocation, it provides a way to increase the number of TIOT/JFCB entries that are created, so that more volumes can be dynamically allocated as required during the lifetime of the allocation. For VSAM data sets, the Dynamic Volume count is the maximum number of volumes that all components in the sphere being allocated can span.

Note: Dynamic volume count support when a data set extends is a function of access method end-of-volume (EOV) processing and not the data set type. For products that do not use the standard IBM® access method EOV interface for their data sets, DVC may not be supported. Please consult with your product representative to see if it supports dynamic volume count.

All the following must be true for the Dynamic Volume Count value to be valid:

• The Dynamic Volume Count is larger than the current volume count of the data set.
• The data set is SMS-managed.
• The Space Constraint Relief value is Y.

Dynamic Volume Count is not supported for the following:

• Non-SMS managed data sets or data sets with no associated data class
• System data sets:
  • Page data sets
  • Single-volume data sets such as a catalog BCS or VVDS, VSAM temporary data sets, or any system data set with ACBSDS=ON
• SAM striped data sets
• VSAM data sets with the IMBED or KEYRANGE options
• VSAM EOV Snapshot processing

The Dynamic Volume Count field has significance only when it is larger than administrator-specified data class Volume Count, and any user-specified volume information provided by JCL, IDCAMS, or TSO.

For VSAM data sets associated with a data class with a dynamic volume count that is greater than 1, users must have ALTER access to the RACF resource that protects the data sets.

Compaction

Specifies whether data is to be compressed. You can compress data on tape, or on DASD if the data set is allocated in the extended format. This field is ignored for DASD data sets if the data set name type is not EXT. A compressed data set cannot reside on the same cartridge as a data set that is not compressed.

For physical sequential data sets, you can specify one of the following:

Y

Extended format data sets are compressed and tape volumes are compacted, but the type of DASD compression depends on the COMPRESS option in the IGDSMSxx PARMLIB member.

N

Data sets are not compressed. Tape volumes are not compacted, unless requested by the user on JCL/dynamic allocation. This is the default, if left blank.

T

Extended format data sets are compressed using tailored dictionaries.

G

Extended format data sets are compressed using generic dictionaries.

ZR

Indicates "zEDC Required", meaning that the system should fail the allocation request if the zEDC function is not supported by the system, or if the minimum allocation amount requirement is not met.

ZP

Indicates "zEDC Preferred", meaning that the system should not fail the allocation request, but rather create either a tailored compressed data set if the zEDC function is not supported by the system, or a non-compressed extended format data set if the minimum allocation amount requirement is not met.

T, G, ZR, and ZP override the compression option set in the IGDSMSxx PARMLIB member, and let you select the type of compression on a data set level. Current users of generic compression can move to using tailored or zEDC compression one data set at a time, as new data sets are created.

Spanned / Nonspanned

Specifies whether a data record can span control interval boundaries. This applies to both system-managed and non-system-managed data sets. Specify one of the following:

Spanned

Specifies that if the size of a data record is larger than a control interval, the record can be contained on more than one control interval. This lets VSAM select a control interval size that is optimum for the DASD.

When a data record that is larger than a control interval is put into a cluster defined for spanned record format, the first part of the record fills a control interval. Subsequent control intervals are filled until the record is written into the cluster. Unused space in the record's last control interval is not available to contain other data records.

Restriction: Do not use this attribute for a variable-length relative record data set (VRRDS).

Nonspanned

Specifies that a record must be contained in one control interval. VSAM selects a control interval size that accommodates the largest record in the data set. This is the default.

System Managed Buffering

specifies the amount of virtual storage for SMB Direct Access Bias obtained for buffers when opening the data set. The possible values are:

• 1K to 2048000K
• 1M to 2048M

System Determined Blocksize

Specifies whether DADSM or OPEN is to use system-determined block size processing:

Y

System-determined block size processing is used only when there is no block size specified on the JCL DD statement, DCB, DCBE and in the DCB OPEN exit routine.

N

No change in block size processing. N (No) is the default.

EATTR

A data set level attribute specifying whether a data set can have extended attributes (format 8 and 9 DSCBs) and optionally reside in EAS.

NO

No extended attributes. The data set can not have extended attributes (format 8 and 9 DSCBs) and cannot reside in EAS. This is the default behavior for non-VSAM data sets.

OPT

Extended attributes are optional. The data set can have extended attributes (format 8 and 9 DSCBs) and can optionally reside in EAS. This is the default behavior for VSAM data sets.

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