Achieving High Transfer Rates to Disk

Achieving High Transfer Rates to Disk

A data collection system can exploit two features to achieve a high rate of data transfer to disk,

asynchronous disk I/O
Guaranteed-rate I/O (GRIO), a feature of the XFS filesystem

Asynchronous I/O that conforms to POSIX 1003.1b-1993 is a standard feature of IRIX. You use asynchronous I/O library calls to initiate disk I/O in a separate process, while your real-time process continues to work with the input data. (In fact you can start asynchronous I/O to any device, not only to disk files.) You can ensure that the asynchronous process performing the I/O executes on a different CPU than the one used by the real-time process.

Using GRIO, your real-time program can claim a specified portion of the bandwidth of a device. I/O requested by other processes is deferred, if necessary, to ensure that your process achieves the promised data rate.

For details of both these features, see Chapter 8, "Optimizing Disk I/O for a Real-Time Program."