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Optimal Storage Aware Caching Policies for Content-Centric Clouds

Caches in Content-Centric Networks (CCN) are increasingly adopting flash memory based storage. The current flash cache technology stores all files with the largest possible expiry date, i.e. the files are written in the memory so that they are retained for as long as possible. This, however, does not leverage the CCN data characteristics where content is typically short-lived and has a distinct popularity profile. Writing files in a cache using the longest retention time damages the memory device thus reducing its lifetime. However, writing using a small retention time can increase the content retrieval delay, since, at the time a file is requested, the file may already have been expired from the memory. This motivates us to consider a joint optimization wherein we obtain optimal policies for jointly minimizing the content retrieval delay (which is a network-centric objective) and the flash damage (which is a device-centric objective). Caching decisions now not only involve what to cache but also for how long to cache each file. We design provably optimal policies and numerically compare them against prior policies.