- High Used RBA (HURBA) (Figure 3)
- Total number of strings assigned (Figure 4).
To compute the number of records in the IS, you need to obtain the information from a LISTCAT for the file and follow these detailed steps:
1. Compute the number of Control Areas (CAs) in the file. The number of CAs is equal to the number of SSI records (lowest-level index):
High Used Data RBA = Total number of CAs in the file Data CISZ * Data CI/CA
2. Locate the number of index records in the file and, using the above result, compute:
# Index records - # of CAs in the file = Total # if IS records
3. The total number of IS records from the above formula represents the minimum additional BUFNIs required for the file. Using the above figure, compute:
# File strings + # of IS records = Total # of required BUFNIs
Once you’ve determined the number of IS records in the file, add this result to the total number of strings to determine the number of BUFNIs required to hold the IS and the associated SSI records. Note that each string requires one index buffer to handle the SSI record. So, the number of strings is used to adjust the formula results from the final step.