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Storage Management Subsystem is an optional feature of Multiple Virtual Storage which is used to improve the management of available disk space in the data center.

In Job control subsystem, normally the developer must specify allocation attributes of datasets, such as the size and location about the data sets, to the operating systems. If they don’t allocate files correctly, this can lead to wasted disk space, and makes it difficult to manage the Direct Access Storage Device in the data center.

Advantage of SMS:

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SMS managed datasets have several advantages,

1. Users are relieved of making decisions about the resource allocation of datasets, since it is handle by SMS.

2. SMS provides the capability of concentrating data sets of unlike devices.

3. SMS managed data sets cannot be deleted unless they are first uncataloged. Due to this extra step, erroneous deletion of data sets is minimized.

4. VSAM data sets created in an SMS environment offer more flexibility than those created through JCL in non-SMS environment.

SMS Constructs:

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With SMS, a new data set can have one or more of the following three constructs:

1. DATA CLASS: Contains the dataset attributes related to allocation of the data set.

2. MANAGEMENT CLASS: Contains the data set attributes related to the migration and backup of the data set. A management class can be assigned to a data set that also has a storage class assigned.