# Amphishea: A Novel Persistent Buffer Management Strategy to Improve SMR Disk Performance
## 7 Conclusions  
SMR disks are expected to be an essential component in future mass data storage systems due to their low cost and high capacity. This paper proposes a CMR-based persistent buffer management strategy called Amphisbaena that can effectively improve the I/O performance of SMR disks under write-intensive workloads. First, a two-phase data block classification method is proposed, which can effectively capture blocks with frequent updates and long update periods, thus reducing redundant RMW operations. Second, a locality-aware buffer space management mechanism is introduced, which achieves a balance between cleaning efficiency and space utilization by dynamically managing buffer blocks with different locality characteristics. Finally, a latency-sensitive garbage collection mechanism is designed to reduce the queuing time of user requests by employing a customized cleanup pattern, splitting the garbage collection process, and detecting write requests to victims. The experimental results are encouraging, the proposed strategy reduces the average I/O latency by 29.9% and RMW operations by 37% compared to the current state-of-the-art strategy.  
Although Amphisbaena has improved the write performance of SMR disks by reducing redundant RMW operations, it still suffers from the following limitations: Firstly, Amphisbaena is designed for write-intensive or read-write-balanced workloads, for read-intensive workloads, it fails to reduce the latency of response to hot-read data. Secondly, when the capacity of the persistent buffer is considerably large, recording the ghost blocks and shadow blocks incurs more memory overhead. With the popularity of high-performance non-volatile storage devices, using them to selectively cache hot-read data and metadata is a cost-effective solution to the above problems. Therefore, we propose to leave effective designs for future work to further increase the versatility of SMR disks in different application scenarios.  
Conceptualization, C.Z.; methodology, C.Z. and F.Y.; software, C.Z. and F.Y.; validation, C.Z., S.N., S.L. and W.T.; formal analysis, C.Z., S.N., S.L. and W.T.; investigation, C.Z., S.N., S.L. and W.T.; resources, C.Z., W.W. and F.L.; data curation, C.Z. and F.Y.; writing--original draft preparation, C.Z.; writing--review and editing, C.Z., S.N. and W.T.; visualization, C.Z. and F.Y.; supervision, F.L. and W.W.; project administration, S.L., W.W. and F.L.; funding acquisition, S.L., S.N., W.W. and F.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (No. 61972311, 62202368), partially by ByteDance Inc (No. PJ20220608900030) and Shandong Provincial Natural Science Foundation (No. ZR2021 LZH009).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.  
Authors [PERSON] and [PERSON] were employed by the company ByteDance Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.