How a Data Class change affects existing Datacom database files

Products

• Datacom
• Datacom/AD
• Datacom/DB

Issue/Introduction

After creating and loading a number of Datacom database files, we noticed that the Data Class we used did not have all the attributes defined as noted in the documentation section Setting Up a Data Class and Allocating Linear Datasets. 

Once we make the changes to the Data Class definition in ISMF, will we need to do anything with the existing files, or will they pick up these changes so we meet the Datacom requirements?

Resolution

First, the Data Class is used when a file is defined, so later changes to the Data Class will not affect existing files. According to the IBM documentation topic Using Data Classes in DFSMS Implementing System-Managed Storage (emphasis added):

A data class is a collection of allocation and space attributes that you define. It is used when data sets are created. You can simplify data set allocation for your users by defining data classes that contain standard data set allocation attributes. You can use data classes with both system-managed and non-system-managed data sets, but some data class characteristics are only available with system-managed requests.

Data class attributes define space and data characteristics of data sets that are normally specified on JCL DD statements, TSO/E ALLOCATE commands, access method services (IDCAMS) DEFINE commands, dynamic allocation requests, and ISPF/PDF panels. For tape data sets, data class attributes can also specify the type of cartridge and recording method, and if the data is to be compacted. Users then need only specify the appropriate data classes to create standardized data sets.

You can use data class to allocate sequential and VSAM data sets in extended format for the benefits of compression (sequential and VSAM KSDS), striping, and large data set sizes (VSAM).

Now, for your existing files, you should run a LISTCAT ALL report on the files, and as long as you don't have any conflicts with the required attributes (as shown in the Setting Up a Data Class and Allocating Linear Datasets page, and in the Requirements section of the page above that), then you are fine to leave them as is. Be aware that there are more than just the DataClass attributes defined, so you would have to use the Listcat to confirm things like the blocksize, shareopts, etc.

If you would be more comfortable to reload them than keep them as is, you can use Online Area Move (OAM) to allocate a new file with the new DataClass and then migrate to that. You can also run a Physical backup, then IDCAMS  delete and define followed by a DBUTLTY INIT, and then reload them.

Additional Information

As always, please contact Broadcom support for Datacom if you have further questions.