# Amphishea: A Novel Persistent Buffer Management Strategy to Improve SMR Disk Performance
## 3 Related Work  
Optimizing the persistent buffer management strategies is one of the most important ways to improve SMR disk performance [7]. There have been many studies discussing how to reduce the cost of persistent buffer cleanup, focusing on two aspects: (1) persistent buffer data layout scheme; and (2) persistent buffer cleanup activity scheduling.  
**Persistent buffer data layout scheme.** Most previous studies have focused on optimizing the SMR-based persistent buffer. For example, as a track-level data cleanup strategy, SACE [36] always prioritizes the eviction of RMW-free victims to reduce write amplification. [PERSON] et al. [12] proposed a strategy called \(SWC^{2}\), which uses a combination of static and dynamic mapping to route data with different update frequencies to the appropriate buffer bands to reduce the cleanup burden. [PERSON] et al. [11] observed that hot blocks that are written back frequently invite a large number of RMWs. To do this, they suggested dividing the persistent buffer into a hot block area and a cold block area and resizing both periodically. A persistent buffer management strategy called KFR [37] uses a redesigned disk layout and allocation unit to divide zone-scale space recovery into several smaller granular k-frames, which effectively reduces the performance recovery time of the disk. Moreover, [PERSON] et al. [13] proposed a host-controllable virtual buffer management scheme that uses a portion of the SMR zones as a virtual buffer to share the write traffic of the persistent buffer.  
Recently, the optimization of the data layout scheme for CMR-based persistent buffers has gradually gained attention. dm-zoned [14] is an open-source translation layer developed by Western Digital that uses device-provided CMR zones to build a persistent buffer, thereby enhancing the versatility of HM-SMR disks. \(\mu\)Cache [15] further explores the optimal size of buffer allocation units based on the dm-zoned data layout scheme. Meanwhile, [PERSON] et al. [16] proposed a loopback-based persistent buffer management strategy for hybrid SMR disks. This strategy avoids writing back hot blocks by re-queuing them instead of  
Figure 4: Detailed descriptions of the RMW procedure during persistent buffer cleanup.  
writing them back to the native zone. In addition, some studies have embedded NAND flash in SMR disks to act as a persistent buffer [9,10]. Although flash-based persistent buffers are more effective in improving the performance of SMR disks than magnetic media-based persistent buffers, they also introduce endurance and high-cost issues.  
**Persistent buffer cleanup activity scheduling.** In addition to optimizing the data layout scheme of persistent buffers, several recent studies attempt to explore the optimal timing of persistent buffer cleanup to improve user quality of service (QoS). For example, Idler [38] heuristically induces buffer cleanup based on workload characteristics and persistent buffer occupancy, thereby reducing the frequency of block cleanup. More recently, a handful of works have attempted to use reinforcement learning models to intelligently schedule cleanup activities to reduce long-tail latency [39,40].