낸드 플래시 저장장치의 성능 및 수명 향상을 위한 프로그램 컨텍스트 기반 최적화 기법

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2019. 2. 김지홍.컴퓨팅 시스템의 성능 향상을 위해, 기존의 느린 하드디스크(HDD)를 빠른 낸드 플래시 메모리 기반 저장장치(SSD)로 대체하고자 하는 연구가 최근 활발히 진행 되고 있다. 그러나 지속적인 반도체 공정 스케일링 및 멀티 레벨링 기술로 SSD 가격을 동급 HDD 수준으로 낮아졌지만, 최근의 첨단 디바이스 기술의 부작용으 로 NAND 플래시 메모리의 수명이 짧아지는 것은 고성능 컴퓨팅 시스템에서의 SSD의 광범위한 채택을 막는 주요 장벽 중 하나이다. 본 논문에서는 최근의 고밀도 낸드 플래시 메모리의 수명 및 성능 문제를 해결하기 위한 시스템 레벨의 개선 기술을 제안한다. 제안 된 기법은 응용 프로 그램의 쓰기 문맥을 활용하여 기존에는 얻을 수 없었던 데이터 수명 패턴 및 중복 데이터 패턴을 분석하였다. 이에 기반하여, 단일 계층의 단순한 정보만을 활용했 던 기존 기법의 한계를 극복함으로써 효과적으로 NAND 플래시 메모리의 성능 및 수명을 향상시키는 최적화 방법론을 제시한다. 먼저, 응용 프로그램의 I/O 작업에는 문맥에 따라 고유한 데이터 수명과 중 복 데이터의 패턴이 존재한다는 점을 분석을 통해 확인하였다. 문맥 정보를 효과 적으로 활용하기 위해 프로그램 컨텍스트 (쓰기 문맥) 추출 방법을 구현 하였다. 프로그램 컨텍스트 정보를 통해 가비지 컬렉션 부하와 제한된 수명의 NAND 플 래시 메모리 개선을 위한 기존 기술의 한계를 효과적으로 극복할 수 있다. 둘째, 멀티 스트림 SSD에서 WAF를 줄이기 위해 데이터 수명 예측의 정확 성을 높이는 기법을 제안하였다. 이를 위해 애플리케이션의 I/O 컨텍스트를 활용 하는 시스템 수준의 접근 방식을 제안하였다. 제안된 기법의 핵심 동기는 데이터 수명이 LBA보다 높은 추상화 수준에서 평가 되어야 한다는 것이다. 따라서 프 로그램 컨텍스트를 기반으로 데이터의 수명을 보다 정확히 예측함으로써, 기존 기법에서 LBA를 기반으로 데이터 수명을 관리하는 한계를 극복한다. 결론적으 로 따라서 가비지 컬렉션의 효율을 높이기 위해 수명이 짧은 데이터를 수명이 긴 데이터와 효과적으로 분리 할 수 있다. 마지막으로, 쓰기 프로그램 컨텍스트의 중복 데이터 패턴 분석을 기반으로 불필요한 중복 제거 작업을 피할 수있는 선택적 중복 제거를 제안한다. 중복 데 이터를 생성하지 않는 프로그램 컨텍스트가 존재함을 분석적으로 보이고 이들을 제외함으로써, 중복제거 동작의 효율성을 높일 수 있다. 또한 중복 데이터가 발생 하는 패턴에 기반하여 기록된 데이터를 관리하는 자료구조 유지 정책을 새롭게 제안하였다. 추가적으로, 서브 페이지 청크를 도입하여 중복 데이터를 제거 할 가능성을 높이는 세분화 된 중복 제거를 제안한다. 제안 된 기술의 효과를 평가하기 위해 다양한 실제 시스템에서 수집 된 I/O 트레이스에 기반한 시뮬레이션 평가 뿐만 아니라 에뮬레이터 구현을 통해 실제 응용을 동작하면서 일련의 평가를 수행했다. 더 나아가 멀티 스트림 디바이스의 내부 펌웨어를 수정하여 실제와 가장 비슷하게 설정된 환경에서 실험을 수행하 였다. 실험 결과를 통해 제안된 시스템 수준 최적화 기법이 성능 및 수명 개선 측면에서 기존 최적화 기법보다 더 효과적이었음을 확인하였다. 향후 제안된 기 법들이 보다 더 발전된다면, 낸드 플래시 메모리가 초고속 컴퓨팅 시스템의 주 저장장치로 널리 사용되는 데에 긍정적인 기여를 할 수 있을 것으로 기대된다.Replacing HDDs with NAND flash-based storage devices (SSDs) has been one of the major challenges in modern computing systems especially in regards to better performance and higher mobility. Although the continuous semiconductor process scaling and multi-leveling techniques lower the price of SSDs to the comparable level of HDDs, the decreasing lifetime of NAND flash memory, as a side effect of recent advanced device technologies, is emerging as one of the major barriers to the wide adoption of SSDs in highperformance computing systems. In this dissertation, system-level lifetime improvement techniques for recent high-density NAND flash memory are proposed. Unlike existing techniques, the proposed techniques resolve the problems of decreasing performance and lifetime of NAND flash memory by exploiting the I/O context of an application to analyze data lifetime patterns or duplicate data contents patterns. We first present that I/O activities of an application have distinct data lifetime and duplicate data patterns. In order to effectively utilize the context information, we implemented the program context extraction method. With the program context, we can overcome the limitations of existing techniques for improving the garbage collection overhead and limited lifetime of NAND flash memory. Second, we propose a system-level approach to reduce WAF that exploits the I/O context of an application to increase the data lifetime prediction for the multi-streamed SSDs. The key motivation behind the proposed technique was that data lifetimes should be estimated at a higher abstraction level than LBAs, so we employ a write program context as a stream management unit. Thus, it can effectively separate data with short lifetimes from data with long lifetimes to improve the efficiency of garbage collection. Lastly, we propose a selective deduplication that can avoid unnecessary deduplication work based on the duplicate data pattern analysis of write program context. With the help of selective deduplication, we also propose fine-grained deduplication which improves the likelihood of eliminating redundant data by introducing sub-page chunk. It also resolves technical difficulties caused by its finer granularity, i.e., increased memory requirement and read response time. In order to evaluate the effectiveness of the proposed techniques, we performed a series of evaluations using both a trace-driven simulator and emulator with I/O traces which were collected from various real-world systems. To understand the feasibility of the proposed techniques, we also implemented them in Linux kernel on top of our in-house flash storage prototype and then evaluated their effects on the lifetime while running real-world applications. Our experimental results show that system-level optimization techniques are more effective over existing optimization techniques.I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 Garbage Collection Problem . . . . . . . . . . . . . 2 1.1.2 Limited Endurance Problem . . . . . . . . . . . . . 4 1.2 Dissertation Goals . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 Dissertation Structure . . . . . . . . . . . . . . . . . . . . . 7 II. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 NAND Flash Memory System Software . . . . . . . . . . . 9 2.2 NAND Flash-Based Storage Devices . . . . . . . . . . . . . 10 2.3 Multi-stream Interface . . . . . . . . . . . . . . . . . . . . 11 2.4 Inline Data Deduplication Technique . . . . . . . . . . . . . 12 2.5 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1 Data Separation Techniques for Multi-streamed SSDs 13 2.5.2 Write Traffic Reduction Techniques . . . . . . . . . 15 2.5.3 Program Context based Optimization Techniques for Operating Systems . . . . . . . . 18 III. Program Context-based Analysis . . . . . . . . . . . . . . . . 21 3.1 Definition and Extraction of Program Context . . . . . . . . 21 3.2 Data Lifetime Patterns of I/O Activities . . . . . . . . . . . 24 3.3 Duplicate Data Patterns of I/O Activities . . . . . . . . . . . 26 IV. Fully Automatic Stream Management For Multi-Streamed SSDs Using Program Contexts . . 29 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.2.1 No Automatic Stream Management for General I/O Workloads . . . . . . . . . 33 4.2.2 Limited Number of Supported Streams . . . . . . . 36 4.3 Automatic I/O Activity Management . . . . . . . . . . . . . 38 4.3.1 PC as a Unit of Lifetime Classification for General I/O Workloads . . . . . . . . . . . 39 4.4 Support for Large Number of Streams . . . . . . . . . . . . 41 4.4.1 PCs with Large Lifetime Variances . . . . . . . . . 42 4.4.2 Implementation of Internal Streams . . . . . . . . . 44 4.5 Design and Implementation of PCStream . . . . . . . . . . 46 4.5.1 PC Lifetime Management . . . . . . . . . . . . . . 46 4.5.2 Mapping PCs to SSD streams . . . . . . . . . . . . 49 4.5.3 Internal Stream Management . . . . . . . . . . . . . 50 4.5.4 PC Extraction for Indirect Writes . . . . . . . . . . 51 4.6 Experimental Results . . . . . . . . . . . . . . . . . . . . . 53 4.6.1 Experimental Settings . . . . . . . . . . . . . . . . 53 4.6.2 Performance Evaluation . . . . . . . . . . . . . . . 55 4.6.3 WAF Comparison . . . . . . . . . . . . . . . . . . . 56 4.6.4 Per-stream Lifetime Distribution Analysis . . . . . . 57 4.6.5 Impact of Internal Streams . . . . . . . . . . . . . . 58 4.6.6 Impact of the PC Attribute Table . . . . . . . . . . . 60 V. Deduplication Technique using Program Contexts . . . . . . 62 5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.2 Selective Deduplication using Program Contexts . . . . . . . 63 5.2.1 PCDedup: Improving SSD Deduplication Efficiency using Selective Hash Cache Management . . . . . . 63 5.2.2 2-level LRU Eviction Policy . . . . . . . . . . . . . 68 5.3 Exploiting Small Chunk Size . . . . . . . . . . . . . . . . . 70 5.3.1 Fine-Grained Deduplication . . . . . . . . . . . . . 70 5.3.2 Read Overhead Management . . . . . . . . . . . . . 76 5.3.3 Memory Overhead Management . . . . . . . . . . . 80 5.3.4 Experimental Results . . . . . . . . . . . . . . . . . 82 VI. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 6.1 Summary and Conclusions . . . . . . . . . . . . . . . . . . 88 6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.2.1 Supporting applications that have unusal program contexts . . . . . . . . . . . . . 89 6.2.2 Optimizing read request based on the I/O context . . 90 6.2.3 Exploiting context information to improve fingerprint lookups . . . . .. . . . . . 91 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92Docto

SOCIOECONOMIC ISSUES IN IRRIGATION DEVELOPMENT AND DISTRIBUTION

Resource /Energy Economics and Policy,

Runtime Systems for Persistent Memories

Emerging persistent memory (PM) technologies promise the performance of DRAM with the durability of disk. However, several challenges remain in existing hardware, programming, and software systems that inhibit wide-scale PM adoption. This thesis focuses on building efficient mechanisms that span hardware and operating systems, and programming languages for integrating PMs in future systems. First, this thesis proposes a mechanism to solve low-endurance problem in PMs. PMs suffer from limited write endurance---PM cells can be written only 10^7-10^9 times before they wear out. Without any wear management, PM lifetime might be as low as 1.1 months. This thesis presents Kevlar, an OS-based wear-management technique for PM, that requires no new hardware. Kevlar uses existing virtual memory mechanisms to remap pages, enabling it to perform both wear leveling---shuffling pages in PM to even wear; and wear reduction---transparently migrating heavily written pages to DRAM. Crucially, Kevlar avoids the need for hardware support to track wear at fine grain. It relies on a novel wear-estimation technique that builds upon Intel's Precise Event Based Sampling to approximately track processor cache contents via a software-maintained Bloom filter and estimate write-back rates at fine grain. Second, this thesis proposes a persistency model for high-level languages to enable integration of PMs in to future programming systems. Prior works extend language memory models with a persistency model prescribing semantics for updates to PM. These approaches require high-overhead mechanisms, are restricted to certain synchronization constructs, provide incomplete semantics, and/or may recover to state that cannot arise in fault-free program execution. This thesis argues for persistency semantics that guarantee failure atomicity of synchronization-free regions (SFRs) --- program regions delimited by synchronization operations. The proposed approach provides clear semantics for the PM state that recovery code may observe and extends C++11's "sequential consistency for data-race-free" guarantee to post-failure recovery code. To this end, this thesis investigates two designs for failure-atomic SFRs that vary in performance and the degree to which commit of persistent state may lag execution. Finally, this thesis proposes StrandWeaver, a hardware persistency model that minimally constrains ordering on PM operations. Several language-level persistency models have emerged recently to aid programming recoverable data structures in PM. The language-level persistency models are built upon hardware primitives that impose stricter ordering constraints on PM operations than the persistency models require. StrandWeaver manages PM order within a strand, a logically independent sequence of PM operations within a thread. PM operations that lie on separate strands are unordered and may drain concurrently to PM. StrandWeaver implements primitives under strand persistency to allow programmers to improve concurrency and relax ordering constraints on updates as they drain to PM. Furthermore, StrandWeaver proposes mechanisms that map persistency semantics in high-level language persistency models to the primitives implemented by StrandWeaver.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155100/1/vgogte_1.pd

Dynamic Network Security Control Using Software Defined Networking

This thesis develops and implements a process to rapidly respond to host level security events using a host agent, Software Defined Networking and OpenFlow updates, role based flow classes, and Advanced Messaging Queuing Protocol to automatically update configuration of switching devices and block malicious traffic. Results show flow table updates are made for all tested levels in less than 5.27 milliseconds and event completion time increased with treatment level as expected. As the number of events increases from 1,000 to 50,000, the design scales logarithmically caused mainly by message delivery time. Event processing throughput is limited primarily by the message rate of the agent (40 msg./sec.). Additionally, the maximum effective consume rate for the controller indicates this design is capable of supporting up to 380 hosts at one msg./sec. Finally, every event triggered is successfully processed for both experiments resulting in a 100 percent event success rate

Using parse tree validation to prevent SQL injection attacks

An SQL injection attack targets interactive web applications that employ database services. Such applications accept user input, such as form fields, and then include this input in database requests, typically SQL statements. In SQL injection, the attacker provides user input that results in a different database request than was intended by the application programmer. That is, the interpretation of the user input as part of a larger SQL statement, results in an SQL statement of a different form than originally intended. We describe a technique to prevent this kind of manipulation and hence eliminate SQL injection vulnerabilities. The technique is based on comparing, at run time, the parse tree of the SQL statement before inclusion of user input with that resulting after inclusion of input. Our solution is efficient, adding about 3 ms overhead to database query costs. In addition, it is easily adopted by application programmers, having the same syntactic structure as current popular record set retrieval methods. For empirical analysis, we provide a case study of our solution in J2EE. We implement our solution in a simple static Java class, and show its effectiveness and scalability. 1

Active Response Using Host-Based Intrusion Detection System and Software-Defined Networking

This research proposes AHNSR: Active Host-based Network Security Response by utilizing Host-based Intrusion Detection Systems (HIDS) with Software-Defined Networking (SDN) to enhance system security by allowing dynamic active response and reconstruction from a global network topology perspective. Responses include traffic redirection, host quarantining, filtering, and more. A testable SDN-controlled network is constructed with multiple hosts, OpenFlow enabled switches, and a Floodlight controller, all linked to a custom, novel interface for the Open-Source SECurity (OSSEC) HIDS framework. OSSEC is implemented in a server-agent architecture, allowing scalability and OS independence. System effectiveness is evaluated against the following factors: alert density and a selective Floodlight module response types. At the expected operational load of 500 events per second (EPS), results reveal a mean system response time of 0.5564 seconds from log generation to flow table update via Floodlights Access Control List module. Load testing further assesses performance at 10 - 10000 EPS for all tested response modules

South and South-East Asian coastal fisheries: their status and directions for improved management: conference synopsis and recommendations

As a step to address the problems of coastal fisheries in Asia, the WorldFish Center joined forces with fisheries agencies from eight developing Asian countries (Bangladesh, India, Indonesia, Malaysia, The Philippines, Sri Lanka, Thailand and Vietnam) and the Asian Development Bank, to implement a project entitled “Sustainable Management of Coastal Fish Stocks in Asia” (also known as the “TrawlBase” project). The project was implemented between 1998 and 2001. The main achievements of this partnership were: (a) Development of a database called “Fisheries Resource Information System and Tools” (FiRST), which contains trawl research survey data and socioeconomic information for selected fisheries, and facilitates its analysis; (b) Evaluation of the extent of resource decline and over-fishing, both biological and economic, in the region; (c) Identification of the measures needed to manage coastal fisheries in the participating countries, resulting in draft strategies and action plans; and (d) Strengthening of national capacity in coastal fisheries assessment, planning and management

Status and management of tropical coastal fisheries in Asia

Coastal fisheries, Fishery management, Stock assessment, Conferences, Asia,

Customized Interfaces for Modern Storage Devices

In the past decade, we have seen two major evolutions on storage technologies: flash storage and non-volatile memory. These storage technologies are both vastly different in their properties and implementations than the disk-based storage devices that current soft- ware stacks and applications have been built for and optimized over several decades. The second major trend that the industry has been witnessing is new classes of applications that are moving away from the conventional ACID (SQL) database access to storage. The resulting new class of NoSQL and in-memory storage applications consume storage using entirely new application programmer interfaces than their predecessors. The most significant outcome given these trends is that there is a great mismatch in terms of both application access interfaces and implementations of storage stacks when consuming these new technologies. In this work, we study the unique, intrinsic properties of current and next-generation storage technologies and propose new interfaces that allow application developers to get the most out of these storage technologies without having to become storage experts them- selves. We first build a new type of NoSQL key-value (KV) store that is FTL-aware rather than flash optimized. Our novel FTL cooperative design for KV store proofed to simplify development and outperformed state of the art KV stores, while reducing write amplification. Next, to address the growing relevance of byte-addressable persistent memory, we build a new type of KV store that is customized and optimized for persistent memory. The resulting KV store illustrates how to program persistent effectively while exposing a simpler interface and performing better than more general solutions. As the final component of the thesis, we build a generic, native storage solution for byte-addressable persistent memory. This new solution provides the most generic interface to applications, allow- ing applications to store and manipulate arbitrarily structured data with strong durability and consistency properties. With this new solution, existing applications as well as new “green field” applications will get to experience native performance and interfaces that are customized for the next storage technology evolution

Letter from the Special Issue Editor

Editorial work for DEBULL on a special issue on data management on Storage Class Memory (SCM) technologies