User defined allocations take precedence over default Data Classes. For example, if a Data Class specifies an LRECL of 80 bytes, and the JCL allocation specifies an LRECL of 100 bytes, then 100 bytes are allocated. If the Data Class is altered by the storage administrator, attributes previously allocated by the Class remains unchanged. Alterations are only be honored for new allocations.
5.3.1.2 Planning for Implementation
To identify and reference a particular Data Class, a unique one to eight character name is used, for example, DCDBKSDS.
For each group of data sets that have similar attributes, a Data Class can exist, but is not mandatory. An example where it could be used is with DB2 tablespaces, as they have identical allocation characteristics.
Prior to the definition of Data Classes, an analysis of common data types needs to be undertaken. This should include deciding whether to use ACS routines only for their allocation, or allow users (in this case, the DBA) to assign them as well. There may be a requirement to standardize naming conventions, and agree upon default space allocations.
Attributes include many of the data set characteristics specified on JCL statements, and IDCAMS DEFINE commands. Only those applicable to a particular data set type should be coded, all others should be left blank. Table 8 on page 39 shows a list of attributes for consideration.
Table 8. Data Class Attributes
ATTRIBUTE | COMMENT |
|
|
Data set | - VSAM type (KSDS, ESDS, RRDS or LINR) |
Organization | - Non VSAM type (Sequential, partitioned) |
| - Record format (RECFM) |
| - Logical record length (LRECL) |
| - Key Length (VSAM) |
|
|
Space requirements | - Average record length value |
| - Size of primary allocation |
| - Size of secondary allocation |
| - Number of directory blocks, if a library |
|
|
VSAM, data and volume | - Size of Control Interval and Control Area |
specifics | - Percentage freespace |
| - Replicate |
| - Imbed |
| - Share |
| - Backup while open |
| - Extended addressability |
| - Reuse |
| - Space constraint relief |
| - Spanned/non spanned |
| - Initial load (speed and recovery) |
|
|
5.3.2Storage Class
5.3.2.1Description
Prior to SMS, critical and important data sets that required improved performance or availability were allocated to specific volumes manually. Data sets that required low response times were placed on low activity volumes, where caching
Storage Management with DFSMS 39
