The database engine can use an I/O technique that forces blocks to be written directly from the buffer pool to disk. This optional technique prevents writes to disk from being deferred by the operating system's buffer manager.

In general, use Direct I/O only if you are experiencing memory shortages. In many cases the normal buffered I/O will provide better performance. Test the performance impact before implementing Direct I/O on a production database.

To use this feature, specify the Direct I/O (-directio) startup parameter. If you use the -directio startup parameter, you might need to add additional APWs to compensate for the fact that with Direct I/O, each database write requires more processing time from the APWs.