Acknowledgments ................................................ xi
Foreword 1 ................................................... xiii
Pierre Ficheux
Foreword 2 ..................................................... xv
Maryline Chetto
Part I. Introduction ............................................ 1
Chapter 1. General Introduction ................................. 3
1.1 The outburst of digital data ............................... 3
1.2 Performance and power consumption of storage systems ....... 4
1.3 Memory hierarchy and storage technology .................... 6
1.4 Introduction to flash memory integration ................... 8
1.5 Scope of the book ......................................... 11
1.6 Target audience ........................................... 11
1.7 Outline of the book ....................................... 12
1.8 How to read this book ..................................... 13
Chapter 2. Flash Memories: Structure and Constraints ........... 15
2.1 General presentation of flash memory ...................... 16
2.1.1 The different types of flash memory ................ 16
2.1.2 Operating physical principles ...................... 16
2.1.1 Simplified hierarchical architecture of a NAND
flash memory chip .................................. 18
2.1.4 Operations on flash memory ......................... 21
2.2 Constraints and limitations ............................... 24
2.2.1 Erase-before-write constraint ...................... 24
2.2.2 Wear constraint .................................... 25
2.2.3 Reliability limitation ............................. 26
2.3 Flash memory constraint management systems: general
concepts .................................................. 26
2.3.1 Management of erase-before-write constraint ........ 27
2.3.2 Wear leveling ...................................... 31
2.3.3 Reliability management ............................. 32
2.3.4 Constraint management systems ...................... 32
2.4 Conclusion ................................................ 33
Chapter 3. Evaluation of Performance and Power Consumption of
Storage Systems ................................................ 35
3.1 Benchmarking storage systems based on flash memory ........ 36
3.1.1 Micro-benchmarks ................................... 37
3.1.2 Macro-benchmarks ................................... 39
3.1.3 I/O traces ......................................... 41
3.2 Performance and power consumption metrics of storage
systems ................................................... 42
3.2.1 Performance metrics ................................ 42
3.2.2 Power consumption metrics .......................... 44
3.3 Performance and power consumption measurements for flash
memory based storage systems .............................. 44
3.3.1 Performance exploration through measurements ....... 45
3.3.2 Exploration of the power consumption of storage
systems based on NAND flash memory through
measurements ....................................... 47
3.4 Evaluation of performance and power consumption through
simulation ................................................ 48
3.4.1 General concepts ................................... 48
3.4.2 FlashSim ........................................... 50
3.4.3 NandFlashSim ....................................... 52
3.4.4 Other simulators and general comparison ............ 52
3.5 Conclusion ................................................ 52
Part 2. Embedded Domain and File Systems for Flash Memory:
Flash File Systems ............................................. 55
Chapter 4. Flash File Systems .................................. 57
4.1 General presentation of FFSs .............................. 57
4.1.1 Storage management and flash memory constraints .... 58
4.1.2 Embedded constraints and scalability of FFSs ....... 59
4.2 Integration of FFS storage systems in computer systems:
the Linux example ......................................... 60
4.2.1 Linux Virtual File System VFS ...................... 61
4.2.2 NAND driver MTD .................................... 62
4.3 Presentation of the most popular FFSs: JFFS2, YAFFS2 and
UBIFS ..................................................... 63
4.3.1 JFFS2 .............................................. 64
4.3.2 YAFFS2 ............................................. 66
4.3.3 UBI and UBIFS ...................................... 69
4.4 Other state-of-the-art FFSs ............................... 71
4.5 Conclusion ................................................ 73
Chapter 5. Methodology for Performance and Power Consumption
Exploration of Flash File Systems .............................. 75
5.1 General presentation of exploration methodology ........... 76
5.1.1 Methods and tools .................................. 76
5.1.2 Hardware platform .................................. 77
5.2 A toolset for performance exploration of FFS-based
systems on Linux .......................................... 78
5.2.1 Flashmon ........................................... 80
5.2.2 VFSMon and FuncMon ................................. 84
5.3 Exploration of power consumption: Open-PEOPLE platform .... 87
5.4 Conclusion ................................................ 91
Chapter 6. Performance and Power Consumption of Dedicated File
Systems: Experimental Results .................................. 93
6.1 Hardware and driver levels ................................ 93
6.1.1 Performance and power consumption of basic flash
operations ......................................... 94
6.1.2 Impact of the MTD read buffer ...................... 96
6.1.3 Conclusion ......................................... 99
6.2 FFS level - focus on JFFS2 ................................ 99
6.2.1 Read at the FFS level .............................. 99
6.2.2 Write at the FFS level ............................ 108
6.2.3 Conclusion ........................................ 116
6.3 VFS level ................................................ 117
6.3.1 Page cache ........................................ 117
6.3.2 Read-ahead mechanism .............................. 120
6.3.3 The write-back mechanism .......................... 122
6.3.4 Conclusion ........................................ 123
6.4 Conclusion ............................................... 123
Part 3 . Flash Translation Layers ............................. 127
Chapter 7. Flash Translation Layer ............................ 129
7.1 Introduction ............................................. 129
7.2 Basic mapping schemes .................................... 130
7.2.1 Page-level mapping scheme ......................... 131
7.2.2 Block-level mapping scheme ........................ 131
7.2.3 Hybrid mapping scheme ............................. 132
7.3 Complex mapping schemes .................................. 133
7.3.1 Log block FTL ..................................... 134
7.3.2 Page-level mapping FTL ............................ 138
7.3.3 FTL with partitioned flash memory ................. 139
7.4 Wear leveling ............................................ 140
7.4.1 Wear leveling based on the number of erase
operations ........................................ 141
7.4.2 Wear leveling based on the number of write cycles . 142
7.5 Garbage collection algorithms ............................ 142
7.6 Cache mechanisms for flash memory ........................ 144
7.7 Conclusion ............................................... 146
Chapter 8. Methodology for the Evaluation of SSD Performance
and Power Consumption ......................................... 149
8.1 Introduction ............................................. 150
8.1.1 Method and tools .................................. 150
8.1.2 Hardware platform ................................. 151
8.2 I/O software stack in Linux .............................. 151
8.2.1. The generic block layer ........................... 153
8.2.2 The I/O scheduler ................................. 154
8.2.3 The device driver ................................. 156
8.3 Context: the Cloud ....................................... 156
8.4 I/O monitoring tools for performance exploration ......... 157
8.4.1 Level 1: the hypervisor ........................... 158
8.4.2 Level 2: host VFS ................................. 160
8.4.3 Level 3: file system .............................. 162
8.4.4 Level 4: block layer .............................. 162
8.5 Performance and energy consumption analysis .............. 166
8.5.1 Measurement of the overall system (PDU) ........... 166
8.5.2 Measurement of the storage system (sensors) ....... 168
8.6 Conclusion .......................................... 169
Chapter 9. Performance and Power Consumption of SSD Based
Systems: Experimental Results ................................. 171
9.1 Introduction ............................................. 171
9.2 Impact of I/Os on performance and energy consumption ..... 172
9.3 A macroscopic view of performance and power consumption
of storage systems ....................................... 174
9.3.1 Hardware/software configuration for experiments ... 175
9.3.2 Measurement results ............................... 176
9.4 A microscopic view of performance and power consumption
of storage systems ....................................... 185
9.4.1 The use of micro-benchmarks ....................... 185
9.4.2 Video application case study ...................... 190
9.5 Conclusions .............................................. 198
Part 4. Emerging Non-volatile Memories ........................ 201
Chapter 10. Emerging Non-volatile Memories .................... 203
10.1 Introduction ............................................. 203
10.2 NVM integration .......................................... 204
10.2.1 Integration as a storage system ................... 204
10.2.2 Integration as a main memory ...................... 206
10.2.3 Integration in CPU caches ......................... 206
10.3 PCM or phase-change memory ............................... 207
10.3.1 Basic concepts .................................... 207
10.3.2 PCM integration ................................... 208
10.3.3 PCM as a main memory .............................. 208
10.3.4 PCM as a storage system ........................... 209
10.3.5 Open questions .................................... 210
10.4 MR AM or magneto-resistive memory ........................ 211
10.4.1 Basic concepts .................................... 212
10.4.2 MRAM integration .................................. 213
10.4.3 Open questions .................................... 215
10.5 FeRAM or ferroelectric memory ............................ 215
10.5.1 Basic concepts .................................... 216
10.5.2 FeRAM integration ................................. 217
10.6 ReRAM or resistive memory ................................ 218
10.6.1 Basic concepts .................................... 219
10.6.2 ReRAM integration ................................. 221
10.6.3 Open questions .................................... 222
10.7 Conclusion ............................................... 223
Conclusion .................................................... 225
Bibliography .................................................. 229
Index ......................................................... 249
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