# Balloon: An Elastic Data Management Strategy for Interlaced Magnetic Recording
## 5 Performance Evaluation
### I/O Performance Evaluation
#### 5.2.1 Write Performance  
Figure (a)a shows the comprehensive write performance comparison between Balloon and its competitors at medium utilization. Notably, the write performance of Balloon-based IMR disks is consistently the closest to that of CMR disks across different workloads. The similarity in performance between Balloon and MAGIC can be attributed to two factors: First, during the top allocation phase, Balloon and MAGIC dynamically select free top tracks based on the hotness of the bottom tracks. When disk utilization is at a medium level, a number of free tracks are available, making it easy to place data on tracks with low rewrite probability. Second, both strategies utilize the persistent buffer to manage write interference data. At medium utilization, the persistent buffer experiences fewer writes, which reduces the impact of cleanup activities on write performance. Despite these similarities, Balloon still outperforms MAGIC with an average write performance improvement of 5.74%. As shown in Figure (a)a, at high utilization rates, Balloon achieves a significant improvement in IMR disk write latency over its competitors, ranging from 6.3% to 92.4%. Of particular note is the 11.3% average improvement in write performance over MAGIC. The effectiveness of Balloon in improving write performance is attributed to its skillful use of the free top track as buffer tracks and its resilient persistent buffer admission and eviction constraints. In addition, Balloon's lightweight track hotness scoring mechanism periodically discards historical data to adapt to current workload access patterns. The above measures significantly reduce the frequency of track rewrites and the impact of buffer cleanup on write performance.  
In addition, we also focused on the performance gap between Balloon-MS and other competitors without a persistent buffer. As shown in Figure (a)a, Balloon-MS outperforms its competitors under both prn_0 and rsrch_0, achieving an average write performance improvement of 45.9% and 38.9%, respectively, while its write latency is higher than MOM under src2_2 and stg_0. This result is due to the fact that Balloon-MS makes full use of the available tracks to act as buffer tracks, and reclaiming buffer tracks introduces some overhead.  
Figure 9: I/O performance of Balloon vs. competitors at 80% space utilization, where the X-axis represents different workloads and the Y-axis represents write latency, read latency, and average latency normalized to CMR.  
At high utilization rates, as shown in Figure 10a, Balloon-MS consistently outperforms MOM. It is noteworthy that both MOM and Balloon-MS resume RMW operations when the disk reaches full capacity, because there are no free tracks available to store the migrated data or act as buffer tracks. However, unlike MOM, which simply moves interfered data to other top tracks to minimize data rewrites, Balloon-MS proactively uses buffer tracks to migrate hot data to the top tracks, effectively reducing the frequency of track rewrites. This key advantage is responsible for the superior write performance of Balloon-MS over MOM in various high-load scenarios.