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z/OS File Allocation

The TSO/E Logon JCL Procedure will perform file allocations but these are generic to all Users of the procedure, and hence cannot be relied upon to allocate application files or data sets, but files must be allocated before they can be used, and there are two ways of doing this;

Via JCL

The inclusion of an appropriate DD statement in the JCL. This method will be required if executing via IRXJCL rather than IKJEFT01 (TSO).

Dynamically within REXX

This is achieved via the TSO ALLOCATE (ALLOC) command. This method provides consistency across Batch and Foreground TSO execution.

File Allocation Examples for z/OS Systems.

There is no intention to discuss the TSO ALLOCATE command in detail, as it has all the capabilities of the JCL DD statement. but some of the more common examples are included here.

• Allocate an existing file or data set
  
  This does not infer input, merely that the data set exists.
  
  
• Allocate a new file or data set, with explicit attribute definition
  
  This method is consistent with both non-SMS data sets, and the overriding of DATACLAS operands..
  
  
• Allocate a new file or data set based on an existing model
  
  This method assumes that there is a catalogued data set with the required attributes.
  
  
• Allocate multiple new files or data sets with common attributes.
  
  This method uses the TSO ATTRIB command in conjunction with ALLOCATE.