HACache: Leveraging Read Performance with Cache in a Heterogeneous Array

2026-04-02

AI Summary

This work addresses the performance bottleneck in heterogeneous RAID arrays, where disparities in SSD speeds cause slower drives to constrain read throughput while faster drives remain underutilized, particularly under read-intensive workloads. To mitigate this inefficiency, the authors propose a cooperative optimization approach leveraging high-performance SSDs as cache devices. The method formalizes the request-splitting problem and introduces a two-stage dynamic mechanism for adjusting the split ratio of incoming read requests. It further incorporates a hit-rate-driven strategy to adaptively manage cache allocation among SSDs. Evaluated on representative mixed-drive configurations, the proposed technique significantly improves system resource utilization and achieves approximately 35% higher read bandwidth compared to baseline approaches.

Abstract

In cost-sensitive deployments, RAID arrays may combine SSDs with different performance levels. Such heterogeneity arises when aging SSDs degrade yet remain usable, or when failed drives are replaced with new devices of explicitly better performance. While this reduces procurement cost, it creates performance challenges: traditional striping mecahnism distributes requests evenly, but slower SSDs become bottlenecks, leaving faster ones underutilized and limiting overall bandwidth to the slowest drive. To address this, we propose HACache (Heterogeneity Adaptive Cache) for read-intensive workloads. HACache introduces high-performance SSDs as read caches to rebalance request distribution. First, we formalize the request diversion problem and solve it formally. Second, to support optimal diversion ratios searching at runtime, HACache adopts a two-phase request diversion ratio adjustment mechanism. Finally, a cache capacity regulation is adopted to adapt quotas for each backend SSD based on hit rates and request diversion needs. This design maximizes bandwidth utilization. Experiments show HACache improves heterogeneous RAID read performance significantly, with bandwidth gains of about 35\% in typical mixed configurations.

Problem

• heterogeneous storage
• RAID performance
• SSD bottleneck
• read bandwidth
• performance imbalance

Innovation

• Heterogeneous RAID
• Read Caching
• Request Diversion
• Bandwidth Optimization
• SSD Performance