An NVM Aware MariaDB Database System and Associated IO Workload on File Systems

MariaDB is a community-developed fork of the MySQL relational database management system and originally designed and implemented in order to use the traditional spinning disk architecture. With Non-Volatile memory (NVM) technology now in the forefront and main stream for server storage (Data centers), MariaDB addresses the need by adding support for NVM devices and introduces NVM Compression method. NVM Compression is a novel hybrid technique that combines application level compression with flash awareness for optimal performance and storage efficiency. Utilizing new interface primitives exported by Flash Translation Layers (FTLs), we leverage the garbage collection available in flash devices to optimize the capacity management required by compression systems. We implement NVM Compression in the popular MariaDB database and use variants of commonly available POSIX file system interfaces to provide the extended FTL capabilities to the user space application. The experimental results show that the hybrid approach of NVM Compression can improve compression performance by 2-7x, deliver compression performance for flash devices that is within 5% of uncompressed performance, improve storage efficiency by 19% over legacy Row-Compression, reduce data writes by up to 4x when combined with other flash aware techniques such as Atomic Writes, and deliver further advantages in power efficiency and CPU utilization. Various micro benchmark measurement and findings on sparse files call for required improvement in file systems for handling of punch hole operations on files

Cross-Layer Optimization Techniques for Improving Performance and Reliability of NAND Flash-Based Storage Systems

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 김지홍.As the cost-per-bit of NAND flash memory is quickly improved by advanced process technologies and multi-leveling techniques, NAND flash-based storage systems are widely employed from mobile embedded systems to high-end enterprise server systems. Although the advanced process and device techniques have greatly improved the cost-per-bit of NAND flash memory, they have also significantly degraded the performance and reliability of NAND flash memory as key side effects of the advanced techniques. In order for NAND flash-based storage systems to be more broadly used in various computing environments, it is critical to overcome the performance and reliability problems of recent high-density NAND flash memory in a satisfactory fashion. In this dissertation, we argue that cross-layer optimization techniques, which vertically integrate various optimization factors from different design abstraction levels, can play key roles in improving performance and reliability of high-density NAND flash memory. First, we propose read-disturb management techniques which reduce the expensive read-disturb management overheads while maintaining reliability of NAND flash memory. An FTL using the read-disturb management module, called redFTL, alleviates highly skewed read accesses to a small part of NAND flash memory into more balanced read accesses to a large number of blocks, thus reducing data migrations needed for avoiding read-disturb errors. As an extended version of redFTL, we propose an integrated read-disturb management technique, called redFTL+, which fundamentally solves read-disturb problems by exploiting a tradeoff between the read disturbance and write speed. By modifying NAND chips to support multiple read modes with different read voltages and write speeds, redFTL+ intelligently allocates frequently-read data to read-resistant blocks. Since the read disturbance is also proportional to the read time, redFTL+ takes advantage of the difference in the read time among different NAND pages by reallocating read-intensive data to read-resistant pages. Second, we propose data separation techniques which reduce garbage collection overhead. We propose a program context-aware data separation technique, called PDS, which can reduce the garbage collection overhead by exploiting program context hints. By using a program context, which serves as a proper granularity of maintaining data update behavior, PDS helps an FTL gather data with similar update times to the same blocks. As an improved version of PDS, we propose an integrated data separation technique, called IDS, which uses both update history of NAND device and program context hints for predicting data update behaviors. By classifying data based on the cross-layer information, an FTL using IDS can make more dead or near-dead blocks over PDS, thus reducing the garbage collection overhead. In order to evaluate the effectiveness of the proposed techniques, we performed a series of evaluations using both a simulator and an emulator with I/O traces which were collected from various systems. Our experimental results show that cross-layer optimization techniques are more effective over our single-layer optimization techniques. RedFTL+ decreases the read-disturb management overhead on average by 24% over redFTL. The IDS-based FTL decreases the garbage collection overhead on aver-age by 18% over the PDS-based FTL. The evaluation results demonstrate that our cross-layer optimization techniques improve an overall performance of NAND-based storage systems over previous single-layered optimization techniques by reducing overheads from read-disturb management and garbage collection while maintaining the reliability of the storage systems.Contents I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 Read-Disturb Problem . . . . . . . . . . . . . . . . 2 1.1.2 Garbage Collection Problem . . . . . . . . . . . . . 4 1.2 Research Goals and Contributions . . . . . . . . . . . . . . 7 1.3 Dissertation Structure . . . . . . . . . . . . . . . . . . . . . 9 II. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1 NAND Flash Memory . . . . . . . . . . . . . . . . . . . . 11 2.2 System Software for NAND Flash Memory . . . . . . . . . 17 2.3 NAND Flash-Based Storage Devices . . . . . . . . . . . . . 18 2.4 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.4.1 Read-Disturb Techniques . . . . . . . . . . . . . . . 20 2.4.2 Data Separation Techniques . . . . . . . . . . . . . 21 III. A Single-Layered Read Disturb Management Technique . . . 24 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2 Performance Implications of Read Disturbs . . . . . . . . . 28 3.2.1 Effect of Frequent Read Reclaims . . . . . . . . . . 28 3.2.2 Effect of Read Reclaims on Response Time Fluctu- ations . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.2.3 Effect of SSD Read Buffer on Read Reclaims . . . . 31 3.3 Read Disturb Management Techniques . . . . . . . . . . . . 32 3.3.1 Data Distribution Technique . . . . . . . . . . . . . 32 3.3.2 Proactive Data Migration . . . . . . . . . . . . . . . 35 3.4 RedFTL: Read Disturb-Aware FTL . . . . . . . . . . . . . . 35 3.4.1 Overview of RedFTL . . . . . . . . . . . . . . . . . 35 3.4.2 Read-Hot Page Separation . . . . . . . . . . . . . . 37 3.4.3 Good Block Pool Management . . . . . . . . . . . . 38 3.5 Experimental Results . . . . . . . . . . . . . . . . . . . . . 38 IV. An Integrated Approach for Read Disturb Management . . . 43 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.2 Read Disturb Management Techniques . . . . . . . . . . . . 46 4.2.1 Mitigation of Read Reclaims by Read Voltage Scaling 47 4.2.2 Mitigation of Read Reclaims by Read Operation Time Scaling . . . . . . . . . . . . . . . . . . . . . . . . 53 4.2.3 NAND Read-Disturbance Model . . . . . . . . . . . 55 4.3 Design and Implementation of RedFTL+ . . . . . . . . . . . 57 4.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . 57 4.3.2 Dynamic Mode Selection . . . . . . . . . . . . . . . 58 4.3.3 Distributed Migration to RRBs . . . . . . . . . . . . 59 4.3.4 Read-Hotness Detection . . . . . . . . . . . . . . . 61 4.4 Experimental Results . . . . . . . . . . . . . . . . . . . . . 63 V. A Single-Layered Data Separation Technique . . . . . . . . . 70 5.1 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.1.1 Frequency-Based Data Separation . . . . . . . . . . 70 5.1.2 Garbage Collection Using ORA . . . . . . . . . . . 73 5.1.3 Evaluation of Existing Locality-based Heuristic . . . 74 5.2 Correlation between Program Contexts and Updates . . . . 78 5.3 PDS: Program Context-Aware Data Separation Technique . . 82 5.4 Experimental Results . . . . . . . . . . . . . . . . . . . . . 87 VI. An Integrated Data Separation Technique . . . . . . . . . . . 93 6.1 Limitations of Single-Layered Program Context-Aware Data Separation Technique . . . . . . . . . . . . . . . . . . . . . 93 6.2 IDS: Integrated Data Separation Technique . . . . . . . . . 94 6.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . 94 6.2.2 Determination of Update Program Context . . . . . 96 6.2.3 Dynamic Clustering Program Contexts Based On Update Locality . . . . . . . . . . . . . . . . . . . . 96 6.2.4 Managing The Hot Data Associated with An Update Program Context . . . . . . . . . . . . . . . . 103 6.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . 104 VII. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 7.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . 114 7.2.1 Improving QoS of RedFTL+ by Exploiting Program Context Hints . . . . . . . . . . . . . . . . . . 114 7.2.2 Mitigating Read-Disturb Problem by Read Disturb- Aware Read Buffer Management Technique . . . . . 115 7.2.3 Improving Efficiency of Garbage Collection by Adjusting GC Trigger Points . . . . . . . . . . . . . . 115 7.2.4 Improving Performance and Reliability of NAND Flash Memory by Integrating Various Techniques . . 117 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126Docto

FLARE: A design environment for FLASH-based space applications

Designing a mass-memory device (i.e., a solid-state recorder) is one of the typical issues of mission-critical space system applications. Flash-memories could be used for this goal: a huge number of parameters and trade-offs need to be explored. Flash-memories are nonvolatile, shock-resistant and power-economic, but in turn have different drawback: e.g., their cost is higher than normal hard disk and the number of erasure cycles is bounded. Moreover space environment presents various issues especially because of radiations: different and quite often contrasting dimensions need to be explored during the design of a flash-memory based solid-state recorder. No systematic approach has so far been proposed to consider them all as a whole: as a consequence a novel design environment currently under development is aimed at supporting the design of flash-based mass-memory device for space application

Exploring Design Dimensions in Flash-based Mass-memory Devices

Mission-critical space system applications present several issues: a typical one is the design of a mass-memory device (i.e., a solid- state recorder). This goal could be accomplished by using flash- memories: the exploration of a huge number of parameters and trade-offs is needed. On the one hand flash-memories are nonvolatile, shock-resistant and power-economic, but on the other hand their cost is higher than normal hard disk, the number of erasure cycles is bounded and other different drawbacks have to be considered. In addition space environment presents various issues especially because of radiations: the design of a flash- memory based solid-state recorder implies the exploration of different and quite often contrasting dimensions. No systematic approach has so far been proposed to consider them all as a whole: as a consequence the design of flash-based mass-memory device for space applications is intended to be supported by a novel design environment currently under development and refinemen

Flash-memories in Space Applications: Trends and Challenges

Nowadays space applications are provided with a processing power absolutely overcoming the one available just a few years ago. Typical mission-critical space system applications include also the issue of solid-state recorder(s). Flash-memories are nonvolatile, shock-resistant and power-economic, but in turn have different drawbacks. A solid-state recorder for space applications should satisfy many different constraints especially because of the issues related to radiations: proper countermeasures are needed, together with EDAC and testing techniques in order to improve the dependability of the whole system. Different and quite often contrasting dimensions need to be explored during the design of a flash-memory based solid- state recorder. In particular, we shall explore the most important flash-memory design dimensions and trade-offs to tackle during the design of flash-based hard disks for space application