Revisiting TRIM on High-Density Flash-Based Hybrid Storage Systems

Hybrid solid state drives (SSDs) that integrate high-performance (HP) and large-capacity (LC) flash are widely used due to their cost-effectiveness. The TRIM command, which is a popular command in normal SSDs to improve performance and endurance, is also recommended in hybrid SSDs. However, employing TRIM on hybrid SSDs as on normal SSDs will induce performance loss and suboptimal endurance due to the different characteristics of flash in hybrid SSDs. To solve the problem, this article first explores the critical factors of issuing TRIM commands to different flash. Then, this article proposed a differential TRIM method (dTRIM), which suggests performing early TRIM on HP flash and lazy TRIM on high-capacity flash. Specifically, early TRIM will minimize garbage collection costs while lazy TRIM tries to avoid conflicting user requests. Experimental results demonstrate that dTRIM can significantly improve the performance and endurance of hybrid SSDs compared with the state-of-the-arts.