Horizontally Scaling Heterogeneous Storage for Combined Capabilities with PolyStore

To manage storage heterogeneity with diverse characteristics in bandwidth and latency, existing approaches such as caching or tiering , employ a vertically-stacked design by placing faster devices on top of slower devices. However, as the performance between device characteristics becomes blurred with emerging storage media, the philosophy of hierarchy inevitably falls short of fully leveraging the combined bandwidth of multiple devices. In this paper, we propose a horizontally structured storage architecture that leverages the combined capabilities of heterogeneous devices. We introduce PolyStore , a meta layer atop storage medium-optimized file systems that spans userspace and the OS, allowing applications to access multiple storage devices concurrently with transparent, fine-grained data placement. PolyStore maximizes cumulative storage bandwidth and reduces hardware and software bottlenecks without compromising important properties such as sharing and security. Our evaluations show that PolyStore achieves 1.11x - 9.38x performance gains for micro-benchmarks and 1.52x - 2.02x for real-world applications across various device configurations.