Reads and writes: when I/Os aren´t quite the same

Redundant disk arrays are gaining increased attention as a feasible I/O organization. In these I/O systems, reads and writes to the system have different performance implications. A write operation actually results in more than one I/O operation. The I/O system´s performance and its organization hence depends on the relative costs of read/write operations and their relative frequency in I/O workloads. The author characterizes the read/write behavior of I/O workloads and how caches affect these characteristics. The characterization, based on real traces, is expected to give a clearer understanding of the performance implications for the I/O system. It has been a widely held belief that disk caches increase the percentage of write requests going to the disk. It is shown through analysis and simulations that this may not be the case and in some cases the disk cache can decrease the percentage of write requests going to the disk