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Oracle Disk I/O Tuning

Chapter 5: Configuration of Automated Storage Management

• The threaded implementation of asynchronous I/O uses the kernel's light-weight process functionality to simulate asynchronous I/O by performing multiple synchronous I/O requests in distinct threads. This achieves I/O parallelism at the expense of additional CPU usage associated with thread creation and extra context switching overheads. If threaded asynchronous I/O is used very intensively, these costs can add as much as 5% to system CPU usage. For this reason using kernelized asynchronous I/O is a preferred method.

Kernelized Asynchronous I/O, popularly known as KIO, is only available if the underlying file system is uses Oracle Disk Manager (ODM) API, Veritas Quick I/O, or a similar product that routes the I/O via a pseudo device driver that can serve as the locus for asynchronous I/O request completion. Also KIO is available if you use the raw partitions. Many operating systems also require special configuration of device files, device drivers and kernel parameters to enable and tune kernelized asynchronous I/O. It is definitely a complex configuration to achieve Asynchronous IO.

The best news is that the KIO is available with the ASM files automatically.

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