EXTEND (Extend Data or Index Areas) › When to Use › How Space Is Allocated for an EXTEND

How Space Is Allocated for an EXTEND

The additional space into which a database data or index area is to be extended can be allocated in one of four ways:

1. Dynamic allocation is always allowed.

   If you specified a secondary allocation parameter when you originally allocated the data set containing the area, you need not supply an z/OS JCL DD statement when running EXTEND (unless a new volume is being added).

   As long as all secondary allocations for the data set have not already been used and sufficient space exists on the last volume allocated to the area to contain the secondary allocation, the EXTEND function automatically requests another extent that is the size of the original secondary allocation specification. The function initializes this new space and resets the control record for the area accordingly.

2. You can supply an z/OS JCL DD statement with a disposition (DISP=) of SHR or OLD and include a SPACE parameter with a secondary allocation amount. As in the previous case, the EXTEND function causes the allocation of this secondary space amount (provided all secondary allocations have not been exhausted), initializes the new space, and resets the control record.
3. You can cause the EXTEND function to add another disk volume to the data set, allocate additional space on the new volume, and initialize the new space. To do this, you must specify an additional disk volume serial number in the z/OS JCL DD statement.

   Also, there must be less space available on the last volume currently allocated to the data set containing the area than you specify for the secondary allocation. This forces allocation of the next extent on the new volume.

   To use this method:

   1. Uncatalog the data set manually (for example, using IEFBR14).
   2. Extend the data set and specify the following in the JCL:
      • Code a SPACE parameter in the DD statement for the area that has a primary quantity equal to the initial primary allocation amount and specify the secondary quantity with the amount by which to extend the data set.
      • For the VOL=SER information, specify the volumes in the same order by which the file was allocated and extended.
      • With the new volume serial number, specify DISP=(OLD,CATLG).
4. You can move the data or index area to another larger data set on another volume of the same device type. You can do this using a non-CA Datacom/DB utility.

   In this case, the EXTEND function compares information from the IBM Data Extent Block (DEB) to the control record information. EXTEND then formats any new blocks based on the extent information from the DEB. The function updates the control record to reflect the new block count.