Bankshot: Caching Slow Storage in Fast Non-Volatile Memory

Emerging non-volatile storage (e.g., Phase Change Memory, STT-RAM) allow access to persistent data at latencies an order of mag-nitude 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 flash-based 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 soft-ware 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, soft-ware support for tracking dirty data and maintaining meta-data. We find that with hardware support Bankshot can offer upto 5× speedup over conventional caching systems