Two-level cache for distributed system in RAID 5 disk controller

We proposed a two-level disk cache model to achieve higher hit ratios and relieve 'small write problem' in RAID 5 disk controller and to enhance reliability of disk cache using non-volatile memory device for stable data. Especially this model improved utilization of first level cache. The proposed cache system consists of two-level caches with different associativities and different block sizes. The first level cache is a set-mapped cache with small block size that uses a set-associative mapping scheme. A set-mapped cache is reduces conflict miss ratios as compared with conventional direct-mapped cache. And the second level cache is a fully-mapped cache with large block size that uses a fully-associative mapping scheme. The large block sizes as a multiple of small blocks. The aim is to show, in terms of hit ratio and service time, that the two-level cache structure presented in this paper is in fact much improved.