Thermo-GC: Reducing Write Amplification by Tagging Migrated Pages during Garbage Collection

Abstract

Flash memory based solid-state drive (SSD) has been deployed in various systems because of its significant advantages over hard disk drive in terms of throughput and IOPS. One inherent operation that is necessary in SSD is garbage collection (GC), a procedure that selects an erasure candidate block and moves valid data on the selected candidate to another block. The performance of SSD is greatly influenced by GC. While existing studies have made advances in minimizing GC cost, few took advantages of the procedure of GC itself. As GC goes on, valid pages in an erasure candidate block tend to have similar lifetimes that can be exploited to minimize page’s movements. In this paper, we introduce Thermo-GC. The idea is to identify data’s hotness during GC operations and group data that have similar lifetimes to the same block. By clustering valid pages based on their hotness, Thermo-GC can minimize valid page movements and reduce GC cost. Experiment results show that Thermo-GC reduces data movements during GC by 78% and write amplification factor by 29.7% on average, implying extended lifetimes of SSDs.