CSA and ECSA allocation values

Technote (FAQ)


Why does panel "KM2C01D Common Storage Utilization" show different values for CSA allocation and ECSA allocation than values given by RMF STORC?


The system always carves out common storage in 4k chunks (or multiples of 4k). So if a task does a GETMAIN for 5k, then 8k is allocated: 5k goes to the requesting task, and 3k remains allocated but unused. If another task asks for 3k, it will get it from there, but if it asks for 4k or more, then a new 4k chunk is allocated. As a result, after the system has been running for a while, there could be a number of small pieces allocated but unused.

The OMEGAMON panel KM2C01D reports both the 'allocated' and 'in use' values. The values called 'CSA Allocation' and 'ECSA Allocation' show the total allocated value. The 'In Use' number is the amount actually being used by tasks.

The allocation number is important because when that gets to 100%, it's possible that additional requests for CSA/ECSA will not be able to be satisfied using the small carved out pieces (even if the 'In Use' value is less than 100%).

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