Deconstructing on-board disk cache by using block-level real traces

On-board disk cache is an effective approach to improve disk performance by reducing the number of physical accesses to the magnetic media. Disk drive manufacturers are increasing the on-board disk cache size to match the capacity growth of the backend magnetic media. Some disk drives nowadays have a cache of 32 MB. Modern computer systems use large amounts of memory to improve performance, any data brought into host memory will be re-accessed there, not in the on-board disk cache. This feature has a significant impact on the behavior of disk cache. This is because computer systems are complex systems consisting of various components. The components are correlated with each other. Therefore, a specific component cannot be isolated from the overall system when we analyze its performance behavior. This paper employs four block-level real traces to explore the performance behavior of the on-board disk cache by considering the impacts of the cache hierarchy contained in computer systems. The analysis gives three major implications: (1) I/O stream at block-level contains negligible temporal locality. Therefore, read/write cache can only achieve marginal benefits. (2) Static write cache does not achieve performance gains since the write stream does not have too much interference with the read stream. Therefore, it is better to leave the on-board disk cache shared by both the write and read streams. (3) Read cache dominates the contribution to the hit ratio besides prefetch. Thus, it is better to focus on improving the read performance rather than write performance of disk cache.