SSD internal cache management policies: A survey

Abstract

SSDs are now increasingly being adopted as primary nonvolatile storage in diverse domains. The internal caches in the SSDs boost SSD performance, lifetime, and robustness. There are three types of internal caches: data cache and mapping cache in the SSD front-end, and flash-based cache in the SSD back-end; they are designed to meet specific requirements like controlling traffic to the back-end, optimization of response time, improving SSD lifetime etc. The underlying memory technology also influences cache design decisions. This work aims to present a methodological survey of cache management policies for these three types of internal caches in SSD. In particular, our work (a) makes a taxonomical classification of cache management policies for each of the cache types and performs a comparative analysis of the research works in each micro-category, (b) derives a set of guidelines that can be helpful for a future cache designer, and (c) enumerates a number of future research directions for designing an optimal SSD internal cache management policy. Our work is distinct from other studies in that we analyze policies for all three types of SSD internal caches, whereas this has not been done in the prior surveys.