Determining How Many Buffers to Allocate in the JES3 Auxiliary Address Space

Before deciding how many user spool access method (USAM) data buffers to allocate in CSA and how many to allocate in the JES3 auxiliary address space, you need to understand how your decision might affect JES3 performance. Knowing this will help you obtain a distribution of buffers between CSA and the JES3 auxiliary address space that is best for your installation.

By allocating some of these buffers in the JES3 auxiliary address space, you can reduce the amount of CSA that JES3 uses. This means that more CSA will be available for use by other address spaces. Thus, your system might be able to do more work because you can start more address spaces.

On the other hand, it takes more time for JES3 to move data between a user address space and the JES3 auxiliary address space than it takes to move the same amount of data between a user address space and CSA storage.

JES3 uses the buffers in the JES3 auxiliary address space only when all of the buffers in CSA are in use. For example, if JES3 needs to move data into a USAM buffer and all of the USAM buffers in CSA storage are in use, JES3 uses a USAM buffer in JES3 auxiliary storage. Therefore, the number of buffers you allocate in CSA storage and how often they are used determine how often JES3 must use buffers in the JES3 auxiliary address space.