The system uses data space (permanent, spool, and temporary space) as overhead for multiple purposes.
- Each cylinder has 2 cylinder indexes.
- Each cylinder index is 32 KB (64 sectors) in size.
- Each cylinder is 23,232 sectors in size.
The quantity of permanent data table space, temporary space, and spool space available on a system is also limited by the amount of disk space required by WAL to process update transactions. The amount of disk required by WAL is a function of the number of update operations being undertaken by the workloads running on the system at any given time, and waxes and wanes. The more simultaneous updates, the greater the quantity of WAL data produced. The amount of WAL data produced is roughly equivalent to twice the amount of transient journal information required for updates.
Allow space for data table overhead as listed in the following table:
| Number of Cylinders | Purpose |
|---|---|
| 13 | General One cylinder each for the following purposes:
Nine cylinders for the following purpose:
The additional cylinders for WAL are required to make sure that MiniCylPack is able to run in low disk situations to free space. |
| Approximately 1.25% of the available data space (minimum) | Cylinder indexes |
| A minimum of 7% free space per cylinder | Fragmentation You must be careful not to allow too much free space for fragmentation, but you must be equally careful not to allow too little. The most practical way to establish an optimal number of cylinders to reserve for fragmentation on your system is trial and error. |
| Ranges between 1 and 20 per pdisk. | Depot The number of cylinders assigned to Depot is set at startup. The value for your system can only be changed by Teradata Support personnel. |