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What is DFSMS? z/OS DFSMS Using the Interactive Storage Management Facility SC23-6856-00 |
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DFSMS is a component of DFSMSdfp. Your storage administrator uses DFSMS to assign various attributes to your data sets and objects so that the system can automatically assume storage management tasks that were previously done manually. DFSMS helps your storage administrator simplify storage management and makes more efficient use of your system space and resources. For more information about DFSMS, refer to z/OS DFSMSdfp Storage Administration. The ISMF applications to which you have access control different
aspects of a data set's allocation or object's creation and performance:
To use DFSMS, your storage administrator designs a configuration that contains sets of attributes, which are called constructs, of the various class and group applications. The storage administrator can create any number of constructs for each DFSMS application, giving each construct a unique name. For example, the storage administrator can define a storage class for data sets or objects that require high performance and another storage class for standard performance. The storage administrator can add, delete, copy, or alter classes as needs change. After defining the necessary constructs, the storage administrator writes automatic class selection (ACS) routines to assign constructs to data sets and objects and to manage data sets and objects. When a new data set is allocated or an object is to be written, DFSMS invokes ACS routines to assign a configuration of DFSMS classes to the data set or object. The attributes from the DFSMS classes then govern the space management, performance, and availability of the data set or object from its creation to its deletion. You can display a list of the available data classes, storage classes, and management classes. You can look at the attributes associated with any specific class, but you cannot change any of the attributes. If you have authorization, you can change the name of a storage class and management class associated with any of your DFSMS-managed data sets. If you need to make any other changes, you must ask your storage administrator to make them for you. The rest of this topic gives you a closer look at each of the three applications to which you have access. The Aggregate Group ApplicationAn aggregate group is an SMS construct that uses control information and data set lists to define an application or other group. It consists of backup criteria and a group of data sets selected for backup by the storage administrator according to application or other requirements. Information on how to define aggregate groups can be found in z/OS DFSMSdfp Storage Administration. The aggregate group application allows you to:
The Data Class ApplicationA data class defines the way data sets are allocated. A data class cannot be assigned to an object. Data class attributes are assigned to a data set when it is created. Data class attributes apply to both DFSMS-managed and non-DFSMS-managed data sets. Attributes specified in JCL or equivalent allocation statements override those specified in a data class. Individual attributes in a data class can be overridden by JCL, TSO, IDCAMS, and dynamic allocation statements. You can display a list of available data classes and look at the attributes of a given class. See Listing and Displaying Class Information. A
data class defines the following attributes:
ISMF's online HELP describes each attribute in detail. Data Class ExamplesThe following attributes and their corresponding values show how a data class for general data sets might be defined by your storage administrator. These data class attributes control characteristics typically specified on JCL DD statements, TSO ALLOCATE commands, and elsewhere. This data class might be defined for all system CNTL, DATA, JCL, and OBJ data sets:
A data set with these attributes would be fixed-block and have 80 bytes per record. The allocated primary space would be 80000 bytes and allocated secondary space would be 8000 bytes. The data set would be allocated as an extended sequential data set if possible and would be striped. However, if it were not possible, the data set would be allocated as a non-extended data set and would not be striped. The following example shows the definition of DCVAR, a data class for variable-length text files. This data class might be defined for all system FOIL, SCRIPT, TEXT, and VSBASIC data sets:
A data set with these characteristics is variable-block and has a record length and average value of 255. The allocated primary space is 255000 and the allocated secondary space is 25500. The Management Class ApplicationBy using the management class for a given data set, DFSMShsm can decide how data sets should be backed up, when they should be migrated, and when backup copies should be deleted. The management class attributes for data sets are used each time DFSMShsm is run. Some management class attributes apply to objects and are used during each object storage management cycle. These attributes assign an expiration date, specify if objects are backed up automatically, and specify when to perform a class transition according to object class transition criteria. You can display a list of available management classes and look at the attributes of a given class. See Listing and Displaying Class Information for more information. To assign and change the management class associated with your data set, see Assigning Classes to Data Sets, and Using Line Operators on DFSMS Lists. A management
class defines the following attributes:
ISMF's online HELP describes each attribute in detail. Management Class ExamplesThe following attributes and their corresponding values show how a management class for standard priority application data sets might be defined by your storage administrator:
A data set with these management class attributes:
The copy operation should not be interrupted if an enqueue failure is encountered. The number of versions that can be maintained for an aggregate group cannot exceed 9999 versions. NOLIMIT indicates that the aggregate backup and recovery function will not roll-off old versions if the system attempts to exceed the 9999 version limit. If your installation does not expire old versions and 9999 versions already exist, the ABACKUP operation fails when the system attempts to create a new version. The last remaining version of the aggregate group will be kept for 9999 days. The other versions of the aggregate group will be kept one hundred months. Data sets associated with this management class, whether part of an aggregate group or not, are backed up using the concurrent copy technique if it is available. Otherwise, they are backed up using the standard backup copy technique. The following example shows how the management class for an object might be defined:
An object assigned this management class would be automatically backed up and would expire after seven years (2555 days). Class transition would occur one month after creation. The Storage Class ApplicationThe Storage Class Application lets the storage administrator specify performance objectives and availability attributes that characterize a collection of data sets. For objects, the storage administrator can define the performance attribute Initial Access Response Seconds. A data set or object must be assigned to a storage class in order to be managed by DFSMS. You can display a list of available storage classes and look at the attributes of a given class. For more information, see Listing and Displaying Class Information, Assigning Classes to Data Sets, and Using Line Operators on DFSMS Lists. A storage class defines
the following attributes:
ISMF's online help describes each attribute in detail. Storage Class ExamplesThe following attributes and their corresponding values represent a typical storage class, SCNORM, for most application data sets:
The majority of input and output for these data sets will be READ. Processing of a data set stops if a device failure occurs with the volume that contains the data set. Placement of the data set depends on available pool space. DFSMS allocates volumes. Data sets in this storage class will be allocated on a volume that is supported by concurrent copy. The data transfer rate of the extended sequential data sets in this storage class will be 2 MB/sec. The following attributes and their corresponding values represent a storage class for an object:
An object assigned to this storage class has to be accessible from any storage source within 60 seconds. Assigning Classes to Data SetsAs a TSO or ISPF/PDF user, you can assign classes to your data sets. As a TSO user, when you allocate an DFSMS-managed data set by using the TSO ALLOCATE command, you can have classes defaulted for you oryou can specify the names of the data class, management class, and storage class to be retained with the data set definition. For details on how to specify a class name on the TSO ALLOCATE command, refer to TSO/E V2 Command Reference. As an ISPF/PDF user, when you allocate an DFSMS-managed data set by using the ISPF/PDF DEFINE command, you can have classesdefaulted for you or you can specify names of classes to be retained with the data set. For more information on this command, refer to ISPF and ISPF/PDF Reference Summary. Assigning Classes to ObjectsUsers cannot assign classes to objects. The storage administrator specifies when objects are assigned classes by DFSMS ACS routines. |
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