H2C-Dedup: Reducing I/O and GC Amplification for QLC SSDs from the Deduplication Metadata Perspective
Yunsheng Dong, Boju Chen, Yanqi Pan, Xiangyu Zou, Wen Xia · 2024
QLC SSDs have gained increasing popularity in cloud computing, PCs, and smartphones due to their low prices and high density, but they suffer from extremely limited endurance. Deduplication can convert redundant chunk writes into fine-grained metadata updates, thereby promising to alleviate QLC wear. Nevertheless, our observation shows that existing deduplication approaches cause even more I/Os than non-deduplication systems. We find that the amplification comes from two sources: (1) I/O amplification due to the mismatched granularity between SSD I/O size (e.g., 4--16 KiB page) and deduplication metadata I/O size, and (2) SSD garbage collection (GC) amplification due to deduplication metadata updates for eliminating redundant chunks (i.e., increment reference count). To address the above problem, this paper proposes H2C-Dedup, which employs two essential techniques. First, to address I/O amplification, cold2hot-heating technique utilizes a log-structured metadata I/O scheme, which ensures that the deduplication metadata is flushed until it is accumulated within I/O cache to match with the OS I/O granularity. Second, to address GC amplification, hot2cold-suppression technique divides metadata into hot (e.g., to store reference count) and cold (e.g., to store fingerprint) segments, delta-encoding the hot entries to ensure both hot and cold metadata will not be modified once they are durable. As a result, H2C-Dedup significantly reduces the deduplication-induced I/O and GC amplification. We implement H2C-Dedup based on F2FS. Extensive experiments on the FEMU platform using microbenchmarks and real-world traces indicate that H2C-Dedup can extend to at most 3.3× and 3.4× lifespan while accelerating 26% and 37% I/O performance compared to SmartDedup and HF-Dedupe.