ZMS: Zone Abstraction for Mobile Flash Storage

We propose an I/O stack for ZNS based flash storage in mobile environment, ZMS. The zone interface is known to save the flash storage from two fundamental issues which modern flash storage suffers from: logical-to-physical mapping table size and garbage collection overhead. Through extensive study, we find that realizing the zone interface in mobile environment is more than a challenge due to the unique characteristics of mobile environment: the lack of on-device memory in mobile flash storage and the frequent fsync() calls in mobile applications. Aligned with this, we identify the root causes that need to be addressed in realizing the zone interface in mobile I/O stack: write buffer thrashing and tiny synchronous file update. We develop a filesystem, block I/O layer, and device firmware techniques to address the above mentioned two issues. The three key techniques in ZMS are (i) IOTailor, (ii) budget-based in-place update, and (iii) multi-granularity logical-to-physical mapping. Evaluation on a real production platform shows that ZMS improves write amplification by 2.9–6.4× and random write performance by 5.0–13.6×. With the three techniques, ZMS shows significant performance improvement in writing to the multiple zones concurrently, executing SQLite transactions, and launching the applications.