Lifetime-aware solid-state disk (SSD) cache management for video servers

Solid-state disks (SSDs) are now being used as enterprise storage servers owing to their technical merits such as low power consumption, shock resistance, and excellent random read performance. To handle the large storage requirements for video data, they can be used as a cache for hard disk drives (HDDs) in video servers, but this poses several questions such as (1) which video segments can be cached on SSD, (2) how to guarantee the lifetime of SSD, and (3) how to make combined use of dynamic random-access memory (DRAM) and SSD for caching. We start by introducing the concept of caching gain to express the amount of disk bandwidth saved by caching, and go on to propose three algorithms: (1) a dynamic programming algorithm that allows for segment popularity in determining which videos should have initial segments (prefixes) stored on the SSD; (2) a throttling algorithm, which limits the number of cache replacements to guarantee the specified lifetime while maximizing caching gain using a parametric search technique; (3) an algorithm that determines the intervals between pairs of consecutive requests to be stored on the DRAM. We quantitatively explore the effect of this caching scheme through simulations, which show that: (1) prefix caching is quite effective for disk bandwidth saving, (2) our throttling algorithm guarantees the lifetime of the SSD, and (3) DRAM caching can be effectively combined with SSD caching with the aim of maximizing overall caching gain.