There are many pieces of hardware and software between the actual physical disk and the log writer background process, and any one of them could be the bottleneck. Performance specialists will tell you they have seen everything from broken Ethernet cables and connectors to nearly all IO being routed to a single controller or a host-based adapter (HBA) card.

Expect the IO team to be defensive and possibly very aggressive in response to this news. After all, when millions of dollars are spent on an IO subsystem and the average write takes 50 ms, people get very nervous. Keep stressing that Oracle's sequential IO write requirements have simply exceeded the IO subsystem's capacity, and that people are working to reduce the IO requirements by focusing on Oracle and on the application. You can also show them the IO requirements Oracle is placing on the IO subsystem. Reports similar to the ones shown n Figures 8-10, 8-15, and 8-16 can be very helpful.

Oracle-focused solutions center on reducing redo generation and ensuring the log writer background process is writing efficiently. We want to make sure that when the log writer background process takes the time to issue a write request, it pushes down a large batch of redo. It is much more efficient to perform a single 1MB IO write than to repeatedly perform 512 writes of 2,048 bytes.