InternationalUnder Review2026
HyZNS: A Flexible Hybrid of Zoned and Conventional Namespaces in a ZNS SSD
Doeun Kim, Junmo Seong, Jinyoung Kim, Junill Jang, Hyuck Han, Sooyong Kang
Journal of Systems Architecture
SSD Firmware · Storage Systems
Junmo Seong
I work on the inside of SSDs: FTL features merged upstream into FEMU, HyZNS, a hybrid zoned/conventional SSD I implemented across the stack, and femonitor, a tool that shows what an emulated SSD is doing while it runs.
About
What I Build
I'm a Master's student in the Software Platforms Lab at Hanyang University. My work sits between the operating system and the SSD, where the NVMe interface, the FTL, and NAND behavior meet real workloads. Next, I want to build SSD firmware.
I've contributed FTL-level features to FEMU that are now upstream, including zone reset with channel/way/plane erase latency and DSM/TRIM handling. I implemented HyZNS, a ZNS SSD with a runtime-resizable conventional area, from the emulated device to its host-side FTL in the Linux kernel. And I built femonitor, a monitoring tool that makes an emulated SSD observable; my thesis uses it to find where FEMU diverges from a real ZNS drive and to fix it.
Research
Publications
Research on ZNS SSDs, FTL design, and SSD emulation
InternationalMay 2026
Lifetime-Aware Zone Allocation for ZNS SSDs
Jinyoung Kim, Doeun Kim, Junmo Seong, Hyuck Han, Sooyong Kang
IEEE International Conference on Fog and Edge Computing (ICFEC)
InternationalMay 2026
Practical Monitoring Tool for ZNS SSD Emulator
Junmo Seong, Doeun Kim, Hyuck Han, Sooyong Kang
IEEE International Conference on Fog and Edge Computing (ICFEC)
DomesticKSC 2025 Outstanding Presentation Paper AwardDec. 2025
A Real-time Monitoring Tool for Device-level Analysis in FEMU-based Storage Systems
FEMU 기반 스토리지 시스템의 디바이스 레벨 분석을 위한 실시간 모니터링 툴
Junmo Seong, Doeun Kim, Hyuck Han, Sooyong Kang
Korean Institute of Information Scientists and Engineers, KSC 2025
DomesticDec. 2024
Performance Analysis of DBSCAN Algorithms Using PIM Architecture
PIM 아키텍처를 활용한 DBSCAN 알고리즘 성능 분석
Junmo Seong, Gun Heo, Hyuck Han, Sooyong Kang
Korean Institute of Information Scientists and Engineers, KSC 2024
Background
Education & Experience
Academic background and professional journey
Education
Now
Mar. 2025 – Feb. 2027 (expected)
M.S. in Computer Science
Hanyang University
- •Research Focus: FTL design, ZNS SSDs, SSD emulation, Linux storage stack
- •Thesis (in progress): Improving the fidelity and observability of FEMU for device-level storage analysis
- •Lab: Software Platforms Lab (Advisor: Prof. Sooyong Kang)
Mar. 2021 – Feb. 2025
B.S. in Computer Science
Hanyang University
- •GPA: 4.1/4.5
Experience
2025 – 2026
Teaching Assistant
Hanyang University
Operating SystemsSpring 2025, Spring 2026
- →Migrated the course's xv6 materials from x86 to RISC-V, aligning with MIT's current version
- →Wrote assignments on MLFQ and CFS schedulers, kernel threads, copy-on-write, mmap, and file systems
- →Built an automated grading system for xv6 assignments on GitHub Classroom
Capstone Design2025, 2026
- →2025: mentored a BBSSD vs. ZNS (dm-zap) performance study and dm-zap code improvements
- →2026: mentored dm-lsm, an LSM-tree device-mapper target that runs unmodified ext4/XFS on ZNS SSDs
Sep. 2023 – Feb. 2025
Research Intern
Software Platforms Lab · Hanyang University, Seoul, Korea
- →Implemented and analyzed DBSCAN on the UPMEM Processing-in-Memory architecture, resulting in a published paper (KSC 2024)
- →Developed multi-threaded CPU and CUDA implementations for a study of highly parallel regular-expression matching (published in IEEE Access 2025)
- →Studied FEMU and the Linux kernel I/O stack (VFS, F2FS, block layer, NVMe driver) in depth, laying the groundwork for my SSD research
Work
Projects & Open Source
SSD internals, kernel modules, and open-source work
A ZNS SSD whose conventional (random-write) area can be resized at runtime. Responsible for the overall implementation across the stack
- →FEMU device mode that emulates the hybrid namespace with a movable region boundary
- →dm-hyzns: Linux device-mapper target serving as the host-side FTL (4 KiB page mapping, line-based GC)
- →hyznsd: user-space daemon that grows or shrinks the conventional area on demand
CFEMULinux KernelDevice MapperNVMe ZNSF2FS
Real-time view into an emulated SSD: zone and line states, write pointers, GC and reset counts, per-channel and per-plane utilization, read through vendor-specific NVMe admin commands at under 0.5% overhead
- →Conventional (BBSSD) and ZNS devices side by side for F2FS multi-device setups; ncurses TUI, CSV logging, snapshots
- →Exposed fidelity gaps in FEMU (instant zone resets, unhandled discard, mis-keyed write caches), fixed upstream and validated against a real WD ZN540
- →Basis of my M.S. thesis; used to diagnose double GC in F2FS multi-device setups
CNVMeFEMUQEMUncursesPython
Designed, built, and deployed the official website for the Software Platforms Lab
Next.jsTailwind CSSPostgreSQLPrisma
Built the official website for the IEEE International Conference on Fog and Edge Computing (ICFEC) 2026
Next.jsTailwind CSS
Five merged pull requests: ZNS zone reset with erase latency modeled per channel/way/plane, DSM/TRIM support for the page-mapped FTL (2x fxmark throughput after deletes), a buffer-size fix in the NVMe DSM path, and a fix that keys ZNS write caches by the request's zone
Expertise
Skills
Technical competencies and tools
Languages
CC++PythonTypeScript
SSD Internals
FTLGarbage CollectionNAND latency modelingZNS SSDTRIM / DSMFEMU
Host & Kernel
NVMeNVMe ZNS command setnvme-cliLinux block layerdevice mapperF2FSRocksDB / ZenFS
Benchmark
fiofxmarkdb_benchYCSB
Web
Next.jsReactTailwind CSS