Log-Structured-Merge (LSM) trees are a write-optimized data structure for lightweight, high-performance Key-Value (KV) store. Solid State Disks (SSDs) provide acceleration of KV operations on LSM trees. However, this hierarchical design involves multiple software layers, including the LSM tree, host file system, and Flash Translation Layer (FTL), causing cascading write amplifications. We propose KVSSD, a close integration of LSM trees and the FTL, to manage write amplifications from different layers. KVSSD exploits the FTL mapping mechanism to implement copy-free compaction of LSM trees, and it enables direct data allocation in flash memory for efficient garbage collection. In our experiments, compared to the hierarchical design, our KVSSD reduced the write amplification by 88% and improved the throughput by 347%.

1. KVSSD
Close integration of LSM trees and
flash translation layer for write-efficient KV store
xuanwo

2. Schedule
- Background
- Introduction
- Optimization
- Evaluation
- Industry

3. Key-Value Storage Service

4. Key-Value Storage Service
LSM

5. Write Amplification in Key-Value Storage Service

6. Write Amplification in LSM

7. Write Amplification in File System
● metadata
● journaling
● copy-on-write

8. Write Amplification in FTL

9. Write Amplification in Key-Value Storage Service
LSM tree compaction
File System journaling / CoW
FTL read-modify-write
FTL garbage collection

10. Write Amplification in Key-Value Storage Service
Increase the consumption of storage devices
Reduce write throughput
TCO Increased

11. How to solve Write Amplification?
- LSM tree
- LSM-trie
- PebblesDB
- WiskKey (Titan, badger, AgateDB)
- …
- File System
- Write amplification friendly fs
- More efficient compression algorithm
- Optimization for KV load
- ...

12. How to solve or alleviate Write Amplification?
- Remove FTL
- Open-Channel SSD
- ZNS (Zoned Namespace)
- Add more inside FTL
- Provide Key-Value interface (this paper!)
- Provide Object Storage alike interface
- Computational SSD

13. KVSSD

14. KVSSD - K2P Mapping

15. KVSSD - Remapping Compaction

16. KVSSD - Hot-cold Separation
- write KV pages mapped to the same level to the same flash block

17. KVSSD - Evaluation

18. KVSSD - Evaluation

19. KVSSD - Value
- Lower Write Amplification
- Higher Throughput
- I/O Offload
- Compress / Encrypt / Validation?

20. KVSSD - Industry
- Samsung + SNIA
- 2019@SYSTOR
- https://github.com/OpenMPDK/KVSSD

21. KVSSD - Industry
- NVMe 2.0
- Released at 2021/06/03
- Zoned Namespace Command Set
- Key Value Command Set

22. Thanks!