# Leveraging Static and Dynamic Wear Leveling to Prolong the Lifespan of Solid-State Drives
## 4 Performance Evaluation
### Evaluation of Greedy-MP
Victim block selection policies like CB or WOGC were ineffective in achieving wear leveling when cold data were not distinct. Even when the proportion of cold data was high, while wear leveling was achieved and the average block erase count approached 100, it can be observed that these policies achieve much shorter SSD lifespans compared to the Greedy-MP policy (Figure 6). In particular, the WOGC+PWL policy demonstrates this trend prominently. This is because their low efficiency of a garbage collection leads to a higher frequency of garbage collection. Figure 6: Comparison of SSD Lifespan (PWL, CB+PWL, WOGC+PWL, GREEDY-MP). (**a**) cam01; (**b**) hnm0; (**c**) prm0; (**d**) proj0; (**e**) stga; (**f**) weba. Figure 7: Comparison of Average Block Erase Count at SSD Lifespan Termination (PWL, CB+PWL, WOGC+PWL, GREEDY-MP). (**a**) cam01; (**b**) hm0; (**c**) prn0; (**d**) proj0; (**e**) stga; (**f**) weba. The inefficiency of garbage collection in CB and WOGC-based policies is evident from Figures 8 and 9. Figure 8 shows the average number of valid pages in victim blocks selected for garbage collection in the proj0 and weba traces. Both PWL and Greedy-MP policies, which are based on greedy selection of victim blocks, exhibit relatively low numbers of valid pages. In contrast, when CB and WOGC are used as victim block selection policies, the number of valid pages in victim blocks is significantly higher. Consequently, since fewer clean pages are generated per garbage collection process, more frequent garbage collections are triggered. As a result, as seen in Figure 9, the write amplification factor (WAF) increases. This means that despite processing the same amount of host write requests, more NAND page write operations are incurred internally within the SSD. With a higher number of valid pages in victim blocks, more valid pages need to be moved during each garbage collection operation, and the lower efficiency of garbage collection leads to more frequent garbage collections, thus increasing the WAF. Moreover, in the weba trace, when the initialization ratio is low, meaning the proportion of cold data is low, the WAF of PWL is relatively high. This is due to the imbalance in  
Figure 8: Comparison of Average Valid Pages in Victim Blocks of Garbage Collection (PWL, CB+PWL, WOGC+PWL, GREEDY-MP). (**a**) proj0; (**b**) weba. Figure 9: Comparison of WAF(Write Amplification Factor) (PWL, CB+PWL, WOGC+PWL, GREEDY-MP). (**a**) proj0; (**b**) weba. block erase counts, leading to excessive migrations and ultimately premature bad block occurrence. Consequently, both the average block erase count and the lifespan of the SSD are shortened in this environment (as shown in Figures 6 and 7). In contrast, the Greedy-MP policy exhibits the lowest number of valid pages in victim blocks, indicating higher efficiency in individual garbage collection operations, leading to a lower frequency of garbage collections. As a result, it achieves the lowest WAF, delays bad block occurrence, and achieves a relatively longer SSD lifespan. Finally, Figure 10 compares the average response time of host requests across each trace. The Y-axis of the figure represents the average response time of input/output requests in milliseconds. The results indicate that the Greedy-MP policy consistently exhibits the shortest response time across all traces, alongside the PWL policy which uses a greedy approach for victim block selection. Conversely, the WOGC+PWL policy generally shows the longest response time, with the CB+PWL policy also demonstrating longer response times compared to the Greedy-MP policy. As seen in Figure 8, using WOGC or CB as victim block selection policies results in lower efficiency of garbage collection, leading to an increase in the average response time of input/output requests. In conclusion, the proposed Greedy-MP policy shows no degradation in efficiency of garbage collection compared to the PWL policy, and hence, no significant performance degradation is observed.