Storage guidelines

These storage guidelines help you to determine the approximate amount of below-the-line storage that DFSMShsm requires. Table 1 lists the storage requirements for load modules, storage areas, and other DFSMShsm tasks.
Table 1. Below-the-line storage requirements for load modules, storage areas, and DFSMShsm tasks
Load module, storage area, or DFSMShsm task Storage requirement
DFSMSdss load module 1412KB
System storage 512KB
DFSMShsm static storage 250KB
Each TAPECOPY task 200KB
Each recall task 96KB
Each migration task except secondary space management (SSM) tasks 80KB
SSM control task 62KB + 20(n + 10) bytes, where n is the number of ML1 volumes.
Each SSM migration cleanup task 55KB
Each SSM ML1 to ML2 movement task 97KB
Each backup task 80KB
Each autodump task 80KB
Each data-set recovery task 96KB
IDCAMS load module 80KB
Each recycle task 60KB
Most other DFSMShsm tasks, such as query 50KB

To determine storage required and storage available below the 16 megabyte line, use the following steps:

  1. DFSMShsm static storage, system storage, and the DFSMSdss load module together require a total of 2174KB below-the-line storage. This storage is always needed when DFSMShsm is running.
  2. To calculate available below-the-line storage after DFSMShsm has started, subtract 2174KB from your region size (for this example, region size is 7148KB). 
                            Region size    7148KB
                  Total from step 1  - 2174KB
                                       _______
 
                              Total    4974KB
  3. If, for example, you want to calculate storage that remains available after DFSMShsm migration and backup tasks have been started, multiply the number of migration and backup tasks you are running by the storage required for each task (for this example, use the maximum number of migration and backup tasks, which is 10). 
               Number of migration and backup tasks      10
                 Storage required for each task    x 80KB
 
                                          Total     800KB
  4. Subtract the total storage required for migration and backup tasks from the total remaining storage calculated in step 2. This calculates the remaining available storage in which most other DFSMShsm tasks run. 
                                  Total remaining storage    4974KB
      Total storage required for migration and backup  -  800KB
                                                       _________
 
                                                Total    4174KB
  5. In step 3, you can also use tasks other than migration and backup. You can, for instance, total the storage required for all recall tasks you are going to run, and then find the remaining available storage for migration, backup, and other tasks.