What is the maximum number of extents for a VSAM dataset?

123 extents
A VSAM data set can be expanded to 123 extents per volume. In addition to the limit of 123 extents per volume, these are the other limits on the number of extents for a VSAM data set: If non-SMS-managed, then up to 255 extents per component.

How many extends for a non VSAM dataset?

Non-VSAM Extended Format Normal sequential datasets have a maximum of 16 extents on each volume. Extended datasets increase this to 123 extents. Normal sequential datasets can allocate up to 65,535 tracks on each volume.

How does VSAM calculate file size?

So the file size may be = (rec len x no. of records)/bytes per cylinder. So i will get the space needed for the file in cylinder unit (file size).

What is a VSAM dataset?

Except for linear data sets, VSAM data sets are collections of records, grouped into control intervals. Key-sequenced data set (KSDS) Contains records in order by a key field and can be accessed by the key or by a relative byte address. The key contains a unique value, such as an employee number or part number.

What are extents in JCL?

An extent is a contiguous number of disk drive tracks, cylinders, or blocks. Data sets can increase in extents as they grow. Older types of data sets can have up to 16 extents per volume. Newer types of data sets can have up to 128 extents per volume or 255 extents total on multiple volumes.

How do you read a VSAM dataset?

Use the READ statement to retrieve ( READ ) records from a file. To read a record, you must have opened the file INPUT or I-O . Your program should check the file status key after each READ . You can retrieve records in VSAM sequential files only in the sequence in which they were written.

What is free space in VSAM?

Free space improves performance by reducing the likelihood of control interval and control area splits. This, in turn, reduces the likelihood of VSAM moving a set of records to a different cylinder away from other records in the key sequence.

How does mainframe calculate file size?

LRECL x Number of records – is a rough rule of thumb for total bytes. Another way is to view the file in 3.4 and get the number of tracks used, and assuming you’re on 3390 DASD then multiply the number of tracks by 56664 (no of bytes per track).

What is Listcat in VSAM?

LISTCAT command in VSAM is used to view the properties of VSAM file like volume details, space details, path details, and catalog details. LISTCAT can list many properties like cluster, data, index, spae details, history, volume and much more.

Is VSAM a flat file?

In VSAM files records are stored in control intervals where as in FLAT files records are stored in blocks. FLAT files are sequential read . VSAM files can sequential and random read. In VSAM acess is fast because of organization of records.

Is VSAM still used?

Virtual Storage Access Method (VSAM) is an IBM DASD file storage access method, which was first used in the OS/VS1, OS/VS2 release 1 (SVS) and release 2 (MVS) operating systems. It was later used throughout the Multiple Virtual Storage (MVS) architecture and is now used in the z/OS.

What is unit Sysda in JCL?

Following is the syntax: UNIT=DASD | SYSDA. Where DASD stands for Direct Access Storage Device and SYSDA stands for System Direct Access and refers to the next available disk storage device.