Dynamic Virtual Page-based Flash Translation Layer with Novel Hot Data Identification and Adaptive Parallelism Management

Solid-state disks (SSDs) tend to replace traditional motor-driven hard disks in high-end storage devices in past few decades. However, various inherent features, such as out-of-place update [resorting to garbage collection (GC)] and limited endurance (resorting to wear leveling), need to be reduced to a large extent before that day comes. Both the GC and wear leveling fundamentally depend on hot data identification (HDI). In this paper, we propose a hot data-aware flash translation layer architecture based on a dynamic virtual page (DVPFTL) so as to improve the performance and lifetime of NAND flash devices. First, we develop a generalized dual layer HDI (DL-HDI) framework, which is composed of a cold data pre-classifier and a hot data post-identifier. Those can efficiently follow the frequency and recency of information access. Then, we design an adaptive parallelism manager (APM) to assign the clustered data chunks to distinct resident blocks in the SSD so as to prolong its endurance. Finally, the experimental results from our realized SSD prototype indicate that the DVPFTL scheme has reliably improved the parallelizability and endurance of NAND flash devices with improved GC-costs, compared with related works.Peer reviewe

Exploiting Fine-Grained Spatial Optimization for Hybrid File System Space

Over decades, I/O optimizations implemented in legacy file systems have been concentrated on reducing HDD disk overhead, such as seek time. As SSD (Solid-State Device) is becoming the main storage medium in I/O storage subsystems, file systems integrated with SSD should take a different approach in designing I/O optimizations. This is because SSD deploys the peculiar device characteristics that do not take place in HDD, such as erasure overhead on flash blocks and absence of seek time to positioning data. In this paper, we present HP-hybrid (High Performance-hybrid) file system that provides a single hybrid file system space, by combining HDD and SSD partitions. HP-hybrid targets for optimizing I/O while considering the strength and weakness of two different partitions, to store large-scale amounts of data in a cost-effective way. Especially, HP-hybrid proposes spatial optimizations that are executed in a hierarchical, fine-grained I/O unit, to address the limited SSD storage resources. We conducted several performance experiments to verify the effectiveness of HP-hybrid while comparing to ext2, ext4 and xfs mounted on both SSD and HDD

LSM-tree based Database System Optimization using Application-Driven Flash Management

학위논문(석사)--서울대학교 대학원 :공과대학 컴퓨터공학부,2019. 8. 염헌영.Modern data centers aim to take advantage of high parallelism in storage de- vices for I/O intensive applications such as storage servers, cache systems, and key-value stores. Key-value stores are the most typical applications that should provide a highly reliable service with high-performance. To increase the I/O performance of key-value stores, many data centers have actively adopted next- generation storage devices such as Non-Volatile Memory Express (NVMe) based Solid State Devices (SSDs). NVMe SSDs and its protocol are characterized to provide a high degree of parallelism. However, they may not guarantee pre- dictable performance while providing high performance and parallelism. For example, heavily mixed read and write requests can result in performance degra- dation of throughput and response time due to the interference between the requests and internal operations (e.g., Garbage Collection (GC)). To minimize the interference and provide higher performance, this paper presents IsoKV, an isolation scheme for key-value stores by exploiting internal parallelism in SSDs. IsoKV manages the level of parallelism of SSD directly by running application-driven flash management scheme. By storing data with dif- ferent characteristics in each dedicated internal parallel units of SSD, IsoKV re- duces interference between I/O requests. We implement IsoKV on RocksDB and evaluate it using Open-Channel SSD. Our extensive experiments have shown that IsoKV improves overall throughput and response time on average 1.20× and 43% compared with the existing scheme, respectively.최신 데이터 센터는 스토리지 서버, 캐시 시스템 및 Key-Value stores와 같은 I/O 집약적인 애플리케이션을 위한 스토리지 장치의 높은 병렬성을 활용하는 것을 목표로 한다. Key-value stores는 고성능의 고신뢰 서비스를 제공해야 하는 가장 대표적인 응용프로그램이다. Key-value stores의 I/O 성능을 높이기 위해 많은 데 이터 센터가 비휘발성 메모리 익스프레스(NVMe) 기반 SSD(Solid State Devices) 와 같은 차세대 스토리지 장치를 적극적으로 채택하고 있다. NVMe SSD와 그 프 로토콜은 높은 수준의 병렬성을 제공하는 것이 특징이다. 그러나 NVMe SSD가 병렬성을 제공하면서도 예측 가능한 성능을 보장하지는 못할 수 있다. 예를 들어 읽기 및 쓰기 요청이 많이 혼합되면 요청과 내부 작업(예: GC) 사이의 간섭으로 인해 처리량 및 응답 시간의 성능 저하가 발생할 수 있다. 간섭을 최소화하고 성능을 향상시키기 위해 본 연구에서는 Key-value stores를 위한 격리 방식인 IsoKV를 제시한다. IsoKV는 애플리케이션 중심 플래시 저장장 치 관리 방식을 통해 SSD의 병렬화 수준을 직접 관리한다. IsoKV는 SSD의 각 전용 내부 병렬 장치에 서로 다른 특성을 가진 데이터를 저장함으로써 I/O 요청 간의 간섭을 줄인다. 또한 IsoKV는 SSD의 LSM 트리 로직과 데이터 관리를 동기화하 여 GC를 제거한다. 본 연구에서는 RocksDB를 기반으로 IsoKV를 구현하였으며, Open-Channel SSD를 사용하여 성능평가하였다.. 본 연구의 실험 결과에 따르면 IsoKV는 기존의 데이터 저장 방식과 비교하여 평균 1.20× 빠르고 및 43% 감소된 처리량과 응답시간 성능 개선 결과를 얻었다. 관점에서 43% 감소하였다.Abstract Introduction 1 Background 8 Log-Structured Merge tree based Database 8 Open-Channel SSDs 9 Preliminary Experimental Evaluation using oc bench 10 Design and Implementation 14 Overview of IsoKV 14 GC-free flash storage management synchronized with LSM-tree logic 15 I/O type Isolation through Application-Driven Flash Management 17 Dynamic Arrangement of NAND-Flash Parallelism 19 Implementation 21 Evaluation 23 Experimental Setup 23 Performance Evaluation 25 Related Work 31 Conclusion 34 Bibliography 35 초록 40Maste

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

A Survey on the Integration of NAND Flash Storage in the Design of File Systems and the Host Storage Software Stack

With the ever-increasing amount of data generate in the world, estimated to reach over 200 Zettabytes by 2025, pressure on efficient data storage systems is intensifying. The shift from HDD to flash-based SSD provides one of the most fundamental shifts in storage technology, increasing performance capabilities significantly. However, flash storage comes with different characteristics than prior HDD storage technology. Therefore, storage software was unsuitable for leveraging the capabilities of flash storage. As a result, a plethora of storage applications have been design to better integrate with flash storage and align with flash characteristics. In this literature study we evaluate the effect the introduction of flash storage has had on the design of file systems, which providing one of the most essential mechanisms for managing persistent storage. We analyze the mechanisms for effectively managing flash storage, managing overheads of introduced design requirements, and leverage the capabilities of flash storage. Numerous methods have been adopted in file systems, however prominently revolve around similar design decisions, adhering to the flash hardware constrains, and limiting software intervention. Future design of storage software remains prominent with the constant growth in flash-based storage devices and interfaces, providing an increasing possibility to enhance flash integration in the host storage software stack