2 research outputs found
μ΄κ³ μ©λ μ리λ μ€ν μ΄λ λλΌμ΄λΈλ₯Ό μν μ λ’°μ± ν₯μ λ° μ±λ₯ μ΅μ ν κΈ°μ
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Όλ¬Έ(λ°μ¬) -- μμΈλνκ΅λνμ : 곡과λν μ»΄ν¨ν°κ³΅νλΆ, 2021.8. κΉμ§ν.The development of ultra-large NAND flash storage devices (SSDs) is recently made possible by NAND flash memory semiconductor process scaling and multi-leveling techniques, and NAND package technology, which enables continuous increasing of storage capacity by mounting many NAND flash memory dies in an SSD.
As the capacity of an SSD increases, the total cost of ownership of the storage system can be reduced very effectively, however due to limitations of ultra-large SSDs in reliability and performance,
there exists some obstacles for ultra-large SSDs to be widely adopted.
In order to take advantage of an ultra-large SSD, it is necessary to develop new techniques to improve these reliability and performance issues.
In this dissertation, we propose various optimization techniques to solve the reliability and performance issues of ultra-large SSDs. In order to overcome the optimization limitations of the existing approaches, our techniques were designed based on various characteristic evaluation results of NAND flash devices and field failure characteristics analysis results of real SSDs.
We first propose a low-stress erase technique for the purpose of reducing the characteristic deviation between wordlines (WLs) in a NAND flash block. By reducing the erase stress on weak WLs, it effectively slows down NAND degradation and improves NAND endurance. From the NAND evaluation results, the conditions that can most effectively guard the weak WLs are defined as the gerase mode. In addition, considering the user workload characteristics, we propose a technique to dynamically select the optimal gerase mode that can maximize the lifetime of the SSD.
Secondly, we propose an integrated approach that maximizes the efficiency of copyback operations to improve performance while not compromising data reliability.
Based on characterization using real 3D TLC flash chips, we propose a novel per-block error propagation model under consecutive copyback operations. Our model significantly increases the number of successive copybacks by exploiting the aging characteristics of NAND blocks. Furthermore, we devise a resource-efficient error management scheme that can handle successive copybacks where pages move around multiple blocks with different reliability.
By utilizing proposed copyback operation for internal data movement, SSD performance can be effectively improved without any reliability issues.
Finally, we propose a new recovery scheme, called reparo, for a
RAID storage system with ultra-large SSDs. Unlike the existing RAID recovery schemes, reparo repairs a failed SSD at the NAND die granularity without replacing it with a new SSD, thus avoiding most of the inter-SSD data copies during a RAID recovery step.
When a NAND die of an SSD fails, reparo exploits a multi-core processor of the SSD controller to identify failed LBAs from the failed NAND die and to recover data from the failed LBAs. Furthermore, reparo ensures no negative post-recovery impact on the performance and lifetime of the repaired SSD.
In order to evaluate the effectiveness of the proposed techniques, we implemented them in a storage device prototype, an open NAND flash storage device development environment, and a real SSD environment. And their usefulness was verified using various benchmarks and I/O traces collected the from real-world applications.
The experiment results show that the reliability and performance of the ultra-large SSD can be effectively improved through the proposed techniques.λ°λ체 곡μ μ λ―ΈμΈν, λ€μΉν κΈ°μ μ μν΄μ μ§μμ μΌλ‘ μ©λμ΄ μ¦κ°νκ³ μλ λ¨μ λΈλ νλμ¬ λ©λͺ¨λ¦¬μ νλμ λΈλ νλμ¬ κΈ°λ° μ€ν λ¦¬μ§ μμ€ν
λ΄μ μ λ§μ λΈλ νλμ¬ λ©λͺ¨λ¦¬ λ€μ΄λ₯Ό μ€μ₯ν μ μκ²νλ λΈλ ν¨ν€μ§ κΈ°μ λ‘ μΈν΄ νλλμ€ν¬λ³΄λ€ ν¨μ¬ λ ν° μ΄κ³ μ©λμ λΈλ νλμ¬ μ μ₯μ₯μΉμ κ°λ°μ κ°λ₯νκ² νλ€.
νλμ¬ μ μ₯μ₯μΉμ μ©λμ΄ μ¦κ°ν μλ‘ μ€ν λ¦¬μ§ μμ€ν
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λ³Έ λ
Όλ¬Έμμλ μ΄κ³ μ©λ λΈλκΈ°λ° μ μ₯μ₯μΉ(SSD)μ λ¬Έμ μ μΈ μ±λ₯ λ° μ λ’°μ±μ κ°μ νκΈ° μν λ€μν μ΅μ ν κΈ°μ μ μ μνλ€.
κΈ°μ‘΄ κΈ°λ²λ€μ μ΅μ ν νκ³λ₯Ό 극볡νκΈ° μν΄μ, μ°λ¦¬μ κΈ°μ μ μ€μ λΈλ νλμ¬ μμμ λν λ€μν νΉμ± νκ° κ²°κ³Όμ SSDμ νμ₯ λΆλ νΉμ± λΆμκ²°κ³Όλ₯Ό κΈ°λ°μΌλ‘ κ³ μλμλ€.
μ΄λ₯Ό ν΅ν΄μ λΈλμ νλμ¬ νΉμ±κ³Ό SSD, κ·Έλ¦¬κ³ νΈμ€νΈ μμ€ν
μ λμ νΉμ±μ κ³ λ €ν μ±λ₯ λ° μ λ’°μ±μ ν₯μμν€λ μ΅μ ν λ°©λ²λ‘ μ μ μνλ€.
첫째λ‘, λ³Έ λ
Όλ¬Έμμλ λΈλ νλμ¬ λΆλ‘λ΄μ νμ΄μ§λ€κ°μ νΉμ±νΈμ°¨λ₯Ό μ€μ΄κΈ° μν΄μ λμ μΈ μκ±° μ€νΈλ μ€ κ²½κ° κΈ°λ²μ μ μνλ€. μ μλ κΈ°λ²μ λΈλ λΈλ‘μ λ΄κ΅¬μ±μ λ리기 μν΄μ νΉμ±μ΄ μ½ν νμ΄μ§λ€μ λν΄μ λ μ μ μκ±° μ€νΈλ μ€κ° μΈκ°ν μ μλλ‘ λΈλ νκ° κ²°κ³Όλ‘ λΆν° μκ±° μ€νΈλ μ€ κ²½κ° λͺ¨λΈμ ꡬμΆνλ€. λν μ¬μ©μ μν¬λ‘λ νΉμ±μ κ³ λ €νμ¬, μκ±° μ€νΈλ μ€ κ²½κ° κΈ°λ²μ ν¨κ³Όκ° μ΅λν λ μ μλ μ΅μ μ κ²½κ° μμ€μ λμ μΌλ‘ νλ¨ν μ μλλ‘ νλ€. μ΄λ₯Ό ν΅ν΄μ λΈλ λΈλ‘μ μ΄νμν€λ μ£Όμ μμΈμΈ μκ±° λμμ ν¨μ¨μ μΌλ‘ μ μ΄ν¨μΌλ‘μ¨ μ μ₯μ₯μΉμ μλͺ
μ ν¨κ³Όμ μΌλ‘ ν₯μμν¨λ€.
λμ§Έλ‘, λ³Έ λ
Όλ¬Έμμλ κ³ μ©λ SSDμμμ λ΄λΆ λ°μ΄ν° μ΄λμΌλ‘ μΈν μ±λ₯ μ νλ¬Έμ λ₯Ό κ°μ νκΈ° μν΄μ
λΈλ νλμ¬μ μ νλ μΉ΄νΌλ°±(copyback) λͺ
λ Ήμ νμ©νλ μ μν κΈ°λ²μΈ rCPBμ μ μνλ€.
rCPBμ Copyback λͺ
λ Ήμ ν¨μ¨μ±μ κ·Ήλν νλ©΄μλ λ°μ΄ν° μ λ’°μ±μ λ¬Έμ κ° μλλ‘
λΈλμ λΈλμ λ
ΈννΉμ±μ λ°μν μλ‘μ΄ copyback μ€λ₯ μ ν λͺ¨λΈμ κΈ°λ°μΌλ‘νλ€.
μ΄μλν΄, μ λ’°μ±μ΄ λ€λ₯Έ λΈλκ°μ copyback λͺ
λ Ήμ νμ©ν λ°μ΄ν° μ΄λμ λ¬Έμ μμ΄ κ΄λ¦¬νκΈ° μν΄μ
μμ ν¨μ¨μ μΈ μ€λ₯ κ΄λ¦¬ 체κ³λ₯Ό μ μνλ€. μ΄λ₯Ό ν΅ν΄μ μ λ’°μ±μ λ¬Έμ λ₯Ό μ£Όμ§ μλ μμ€μμ copybackμ μ΅λν νμ©νμ¬ λ΄λΆ λ°μ΄ν° μ΄λμ μ΅μ ν ν¨μΌλ‘μ¨ SSDμ μ±λ₯ν₯μμ λ¬μ±ν μ μλ€.
λ§μ§λ§μΌλ‘, λ³Έ λ
Όλ¬Έμμλ μ΄κ³ μ©λ SSDμμ λΈλ νλμ¬μ λ€μ΄(die) λΆλμΌλ‘ μΈν λ μ΄λ(redundant array of independent disks, RAID) 리λΉλ μ€λ²ν€λλ₯Ό μ΅μν νκΈ°μν μλ‘μ΄ RAID 볡ꡬ κΈ°λ²μΈ reparoλ₯Ό μ μνλ€.
Reparoλ SSDμ λν κ΅μ²΄μμ΄ SSDμ λΆλ dieμ λν΄μλ§ λ³΅κ΅¬λ₯Ό μνν¨μΌλ‘μ¨ λ³΅κ΅¬ μ€λ²ν€λλ₯Ό μ΅μννλ€.
λΆλμ΄ λ°μν dieμ λ°μ΄ν°λ§ μ λ³μ μΌλ‘ 볡ꡬν¨μΌλ‘μ¨ λ³΅κ΅¬ κ³Όμ μ 리λΉλ νΈλν½μ μ΅μννλ©°,
SSD λ΄λΆμ λ³λ ¬κ΅¬μ‘°λ₯Ό νμ©νμ¬ λΆλ die 볡ꡬ μκ°μ ν¨κ³Όμ μΌλ‘ λ¨μΆνλ€.
λν die λΆλμΌλ‘ μΈν 물리μ 곡κ°κ°μμ λΆμμ©μ μ΅μν ν¨μΌλ‘μ¨ λ³΅κ΅¬ μ΄νμ μ±λ₯ μ ν λ° μλͺ
μ κ°μ λ¬Έμ κ° μλλ‘ νλ€.
λ³Έ λ
Όλ¬Έμμ μ μν κΈ°λ²λ€μ μ μ₯μ₯μΉ νλ‘ν νμ
λ° κ³΅κ° λΈλ νλμ¬ μ μ₯μ₯μΉ κ°λ°νκ²½, κ·Έλ¦¬κ³ μ€μ₯ SSDνκ²½μ ꡬνλμμΌλ©°,
μ€μ μμ© νλ‘κ·Έλ¨μ λͺ¨μ¬ν λ€μν λ²€νΈλ§ν¬ λ° μ€μ I/O νΈλ μ΄μ€λ€μ μ΄μ©νμ¬ κ·Έ μ μ©μ±μ κ²μ¦νμλ€.
μ€ν κ²°κ³Ό, μ μλ κΈ°λ²λ€μ ν΅ν΄μ μ΄κ³ μ©λ SSDμ μ λ’°μ± λ° μ±λ₯μ ν¨κ³Όμ μΌλ‘ κ°μ ν μ μμμ νμΈνμλ€.I Introduction 1
1.1 Motivation 1
1.2 Dissertation Goals 3
1.3 Contributions 5
1.4 Dissertation Structure 8
II Background 11
2.1 Overview of 3D NAND Flash Memory 11
2.2 Reliability Management in NAND Flash Memory 14
2.3 UL SSD architecture 15
2.4 Related Work 17
2.4.1 NAND endurance optimization by utilizing page characteristics difference 17
2.4.2 Performance optimizations using copyback operation 18
2.4.3 Optimizations for RAID Rebuild 19
2.4.4 Reliability improvement using internal RAID 20
III GuardedErase: Extending SSD Lifetimes by Protecting Weak Wordlines 22
3.1 Reliability Characterization of a 3D NAND Flash Block 22
3.1.1 Large Reliability Variations Among WLs 22
3.1.2 Erase Stress on Flash Reliability 26
3.2 GuardedErase: Design Overview and its Endurance Model 28
3.2.1 Basic Idea 28
3.2.2 Per-WL Low-Stress Erase Mode 31
3.2.3 Per-Block Erase Modes 35
3.3 Design and Implementation of LongFTL 39
3.3.1 Overview 39
3.3.2 Weak WL Detector 40
3.3.3 WAF Monitor 42
3.3.4 GErase Mode Selector 43
3.4 Experimental Results 46
3.4.1 Experimental Settings 46
3.4.2 Lifetime Improvement 47
3.4.3 Performance Overhead 49
3.4.4 Effectiveness of Lowest Erase Relief Ratio 50
IV Improving SSD Performance Using Adaptive Restricted- Copyback Operations 52
4.1 Motivations 52
4.1.1 Data Migration in Modern SSD 52
4.1.2 Need for Block Aging-Aware Copyback 53
4.2 RCPB: Copyback with a Limit 55
4.2.1 Error-Propagation Characteristics 55
4.2.2 RCPB Operation Model 58
4.3 Design and Implementation of rcFTL 59
4.3.1 EPM module 60
4.3.2 Data Migration Mode Selection 64
4.4 Experimental Results 65
4.4.1 Experimental Setup 65
4.4.2 Evaluation Results 66
V Reparo: A Fast RAID Recovery Scheme for Ultra- Large SSDs 70
5.1 SSD Failures: Causes and Characteristics 70
5.1.1 SSD Failure Types 70
5.1.2 SSD Failure Characteristics 72
5.2 Impact of UL SSDs on RAID Reliability 74
5.3 RAID Recovery using Reparo 77
5.3.1 Overview of Reparo 77
5.4 Cooperative Die Recovery 82
5.4.1 Identifier: Parallel Search of Failed LBAs 82
5.4.2 Handler: Per-Core Space Utilization Adjustment 83
5.5 Identifier Acceleration Using P2L Mapping Information 89
5.5.1 Page-level P2L Entrustment to Neighboring Die 90
5.5.2 Block-level P2L Entrustment to Neighboring Die 92
5.5.3 Additional Considerations for P2L Entrustment 94
5.6 Experimental Results 95
5.6.1 Experimental Settings 95
5.6.2 Experimental Results 97
VI Conclusions 109
6.1 Summary 109
6.2 Future Work 111
6.2.1 Optimization with Accurate WAF Prediction 111
6.2.2 Maximizing Copyback Threshold 111
6.2.3 Pre-failure Detection 112λ°
Extending RSCA for efficient component execution model
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Όλ¬Έ(μμ¬) --μμΈλνκ΅ λνμ :μ κΈ°. μ»΄ν¨ν°κ³΅νλΆ,2006.Maste