DASD Vs. VSAM file Exclusive Differences

Here are five JCL questions asked in an interview. These relate to datasets. Super good questions to refresh these before interviews.

JCL Interview Questions

Q1). Why do we need to use Tape data sets?

A1). We need to use tape datasets to back up the data. Tape datasets we can delete by IDCAMS utility. There are special REXX tools are there to browse Tape datasets

Q2). What is PRTY?

A2). It denotes priority for Output datasets

Q3). How to use DUMMY VSAM dataset?


//ddname DD { DSNAME=data-set-name }
[ ,DISP=(status,normal-disp,abnormal-disp) ]
[ ,AMP=(option,option…) ]

If we mention AMORG in AMP options, we can say that the dataset is VSAM

Q4). Advantage of VSAM over DASD dataset?

A4). It’s important to remember how data access works on DASD (which is the only type of device that can be used for VSAM files). The most time-consuming part of any DASD I/O operation is moving the access mechanism on the device to the record that needs to be read or written. While the actual transfer of data takes place at electronic speeds, the access mechanism movement is a slower, mechanical process

Because of VSAM special file organization they are faster in accessing compared to DASD

Q5). What is the file system in UNIX?

A6). The terms hierarchical file system and HFS are used both for the UNIX file structure in general and for the specific facility that OS/390 uses to manage the files on an IBM mainframe.

HFS files can contain data, executable modules, or UNIX shell scripts that consist of UNIX commands and scripting commands (similar to a procedure). They can also be copied to and from OS/390 sequential, partitioned, or partitioned extended data sets.

Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.