The Harey Tortoise: Managing Heterogeneous Write Performance in SSDs

Recent years have witnessed significant gains in the adoption of flash technology due to increases in bit density, enabling higher capacities and lower prices. Unfortunately, these improvements come at a significant cost to performance with trends pointing toward worst-case flash program latencies on par with disk writes.

We extend a conventional flash translation layer to schedule flash program operations to flash pages based on the operations’ performance needs and the pages’ performance characteristics. We then develop policies to improve performance in two scenarios: First, we improve peak performance for latency-critical operations of short bursts of intensive activity by 36%. Second, we realize steady-state bandwidth improvements of up to 95% by rate-matching garbage collection performance and external access performance.