Step 2. Determine overhead needed for CI resources
If you are using VSAM, you need to determine how much overhead is needed for a CI before you can do the remaining space calculations.
If you are not using VSAM, you can skip this step.
Overhead is space used in a CI for two control fields. VSAM uses the control fields to manage space in the CI. The control fields and their sizes are shown in the following table.
| Field | Size in bytes |
|---|---|
| CIDF (Control interval definition field) | 4 |
| RDF (Record definition field) | 3 |
If one logical record exists for each CI, CI overhead consists of one CIDF and one RDF (for a total of 7 bytes). HDAM and HIDAM databases and PHDAM and PHIDAM partitions use one logical record for each CI.
If more than one logical record exists for each CI, CI overhead consists of one CIDF and two RDFs (for a total of 10 bytes). HISAM (KSDS and ESDS), HIDAM and PHIDAM index, and secondary index databases can all use more than one logical record for each CI.
Step 3 tells you when to factor CI overhead into your space calculations.