Bankshot: caching slow storage in fast non-volatile memory

Abstract

Emerging non-volatile storage (e.g., Phase Change Memory, STTRAM) allow access to persistent data at latencies an order of magnitude lower than SSDs. The density and price gap between NVMs and denser storage make NVM economically most suitable as a cache for larger, more conventional storage (i.e., NAND flashbased SSDs and disks). Existing storage caching architectures (even those that use fast flash-based SSDs) introduce significant software overhead that can obscure the performance benefits of faster memories. We propose Bankshot, a caching architecture that allows cache hits to bypass the OS (and the associated software overheads) entirely, while relying on the OS for heavy-weight operations like servicing misses and performing write backs. We evaluate several design decisions in Bankshot including different cache management policies and different levels of hardware, software support for tracking dirty data and maintaining meta-data. We find that with hardware support Bankshot can offer upto 5x speedup over conventional caching systems.