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KR editions 44 to 46

KR-44 Class

Everyone has surely come across stuff like management class, dataclass and all sorts of classes! Ever wondered what they mean/ how they affect us?

(This KR is a partial repeat of an old one but i felt it would be better to reiterate the main points so that the next few editions will be useful)

These classes are SMS (storage management subsystem) parameters and the classes help in simplifying JCLs (the programmer needn't worry about the DD parameters like UNIT, VOL, LRECL, RECFM etc...).

Each class can take some predefined values (these values are decided by the client). The most frequently encountered classes are:

1.) STORCLAS: This has to be coded to make the data set SMS-managed. This parameter replaces the UNIT and VOL parameter. This is related to storage of the dataset.

2.) DATACLAS: could define any/all of the following parameters: RECFM, LRECL, AVGREC, SPACE, VOL etc...

For example let's say that the admin has defined a DATACLAS called COBOL with RECFM=FB, LRECL=80.

Then in our JCL we can specify DATACLAS=COBOL for a new dataset and SMS will automatically create that dataset with RECFM of FB and LRECL of 80. It's kind of like a substitution (otherwise you would have to specify RECFM=FB,LRECL=80).

Should we always code these SMS parameters in our JCLs? Generally not a must since there will be some default values assigned at the client side (i.e. if you don't specify anything it'll use the default values); but if you want something other than the default then you'll need to code them.

Did you know that we have something called "ISMF" in mainframes!

KR-45 Management Class

There's one more SMS class called Management class (which is quite interesting). We'll also have a look at ISMF.

MGMTCLAS: This parameter isn't used for replacing any DD parameter (only for management of the dataset). Some uses are:

-to determine when the dataset has to be migrated.

-to determine how often a backup of the dataset needs to be created.

-how often the dataset should be compressed, etc...

And now let's step into the practical world of SMS classes.

Type ISMF on the command line in your TSO session and you'll be taken to a whole new world! (Try it now). 
ISMF- Interactive Storage Management Facility is an ISPF application. ISMF will help you understand what the various classes you use in your mainframes actually means. 
Here you can check up what each class used in your system actually means. Basically here you can find a list of all classes (management, storage and data class values permitted by SMS). 

Do explore the options in ISMF- esp. option 3.

KR-46 Management Class (continued)

Let's say that you want to find information about some dataset (let's say xxxx.yyyy.zzzz). Then go into 3.4 option (specify xxxx.yyyy) and you'll get a listing of all datasets starting with xxxx.yyyy. Place an 'i' in the first column before the dataset you are interested in (xxxx.yyyy.zzzz) and you'll get an information screen (which will list all properties about the dataset). Since we are interested in classes; just take a note of the values for the different classes.

Let's say we find that the dataset has a management class of NOBACK10

Now type: START ISMF (on the command line) and you'll be taken to the ISMF panel 

Choose option 3 (Management Class). Since we want to see the properties of NOBACK10; type this in the panel against management class name.

Press enter and you'll be taken to a screen with details on this management class.

The most useful value to check here is the number of days to expire. If it says 10 then it means that datasets created with this management class will be deleted after 10 days. You can also get information about whether backup of these datasets will be done or not. To see a full listing of details; just type DISPLAY in the LINE OPERATOR column.

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