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  1. To bridge the giant semantic gap between applications and modern storage systems, passing a piece of tiny and useful information, called I/O access hints, from upper layers to the storage layer may greatly improve application performance and ease data management in storage systems. This is especially true for heterogeneous storage systems that consist of multiple types of storage devices. Since ingesting external access hints will likely involve laborious modifications of legacy I/O stacks, it is very hard to evaluate the effect and take advantages of access hints. In this article, we design a generic and flexible framework, called HintStor, to quickly play with a set of I/O access hints and evaluate their impacts on heterogeneous storage systems. HintStor provides a new application/user-level interface, a file system plugin, and performs data management with a generic block storage data manager. We demonstrate the flexibility of HintStor by evaluating four types of access hints: file system data classification, stream ID, cloud prefetch, and I/O task scheduling on a Linux platform. The results show that HintStor can execute and evaluate various I/O access hints under different scenarios with minor modifications to the kernel and applications.
    Free, publicly-accessible full text available May 31, 2023
  2. Hybrid Shingled Magnetic Recording (H-SMR) drives are the most recently developed SMR drives, which allow dynamic conversion of the recording format between Conventional Magnetic Recording (CMR) and SMR on a single disk drive. We identify the unique opportunities of H-SMR drives to manage the tradeoffs between performance and capacity, including the possibility of adjusting the SMR area capacity based on storage usage and the flexibility of dynamic data swapping between the CMR area and SMR area. We design and implement FluidSMR, an adaptive management scheme for hybrid SMR Drives, to fully utilize H-SMR drives under different workloads and capacity usages. FluidSMR has a two-phase allocation scheme to support a growing usage of the H-SMR drive. The scheme can intelligently determine the sizes of the CMR and the SMR space in an H-SMR drive based on the dynamic changing of workloads. Moreover, FluidSMR uses a cache in the CMR region, managed by a proposed loop-back log policy, to reduce the overhead of updates to the SMR region. Evaluations using enterprise traces demonstrate that FluidSMR outperforms baseline schemes in various workloads by decreasing the average I/O latency and effectively reducing/controlling the performance impact of the format conversion between CMR and SMR.
  3. Computer systems utilizing byte-addressable Non-Volatile Memory ( NVM ) as memory/storage can provide low-latency data persistence. The widely used key-value stores using Log-Structured Merge Tree ( LSM-Tree ) are still beneficial for NVM systems in aspects of the space and write efficiency. However, the significant write amplification introduced by the leveled compaction of LSM-Tree degrades the write performance of the key-value store and shortens the lifetime of the NVM devices. The existing studies propose new compaction methods to reduce write amplification. Unfortunately, they result in a relatively large read amplification. In this article, we propose NVLSM, a key-value store for NVM systems using LSM-Tree with new accumulative compaction. By fully utilizing the byte-addressability of NVM, accumulative compaction uses pointers to accumulate data into multiple floors in a logically sorted run to reduce the number of compactions required. We have also proposed a cascading searching scheme for reads among the multiple floors to reduce read amplification. Therefore, NVLSM reduces write amplification with small increases in read amplification. We compare NVLSM with key-value stores using LSM-Tree with two other compaction methods: leveled compaction and fragmented compaction. Our evaluations show that NVLSM reduces write amplification by up to 67% compared with LSM-Tree usingmore »leveled compaction without significantly increasing the read amplification. In write-intensive workloads, NVLSM reduces the average latency by 15.73%–41.2% compared to other key-value stores.« less
  4. Deoxyribonucleic Acid (DNA) as a storage medium with high density and long-term preservation properties can satisfy the requirement of archival storage for rapidly increased digital volume. The read and write processes of DNA storage are error-prone. Images widely used in social media have the properties of fault tolerance which are well fitted to the DNA storage. However, prior work simply investigated the feasibility of DNA storage storing different types of data and simply store images in DNA storage, which did not fully investigate the fault-tolerant potential of images in the DNA storage. In this paper, we proposed a new image-based DNA system called IMG-DNA, which can efficiently store images in DNA storage with improved DNA storage robustness. First, a new DNA architecture is proposed to fit JPEG-based images and improve the image’s robustness in DNA storage. Moreover, barriers inserted in DNA sequences efficiently prevent error propagation in images of DNA storage. The experimental results indicate that the proposed IMG-DNA achieves much higher fault-tolerant than prior work.
  5. The total amount of data in the world has been increasing rapidly. However, the increase of data storage capacity is much slower than that of data generation. How to store and archive such a huge amount of data becomes critical and challenging. Synthetic Deoxyribonucleic Acid (DNA) storage is one of the promising candidates with high density and long-term preservation for archival storage systems. The existing works have focused on the achievable feasibility of a small amount of data when using DNA as storage. In this paper, we investigate the scalability and potentials of DNA storage when a huge amount of data, like all available data from the world, is to be stored. First, we investigate the feasible storage capability that can be achieved in a single DNA pool/tube based on current and future technologies. Then, the indexing of DNA storage is explored. Finally, the metadata overhead based on future technology trends is also investigated.
  6. Host-Aware/Drive-Managed Shingled Magnetic Recording (SMR) drives can accept non sequential writes using a buffer called media cache. Data in the media cache will be migrated to its designated location by a cleaning process if the buffer is full (blocking cleaning) or the drive is idle (idle cleaning). However, blocking cleanings can severely extend the I/O response time. Therefore, it is crucial to fully understand the cleaning process and find ways of mitigating the caused performance degradation. In this article we further evaluate the cleaning process and propose a potential remedy scheme called Idler on Host-Aware SMR drives. Idler adaptively induces idle cleanings based on dynamic workload characteristics and media cache usages to reduce the severity of blocking cleanings. Our evaluations show that in the workloads with a small non-sequential write ratio (about 10 percent), Idler can reduce the tail response time and the workload finish time by 56–88 and 10–23 percent, respectively, compared with those without such control. With the help of an external write buffer on an SSD, the tail response time of SMR drives with Idler can be closer to that of conventional disk drives.
  7. Persistent key-value stores are widely used as building blocks in today’s IT infrastructure for managing and storing large amounts of data. However, studies of characterizing real-world workloads for key-value stores are limited due tothe lack of tracing/analyzing tools and the difficulty of collecting traces in operational environments. In this paper, we first present a detailed characterization of workloads from three typical RocksDB production use cases at Facebook: UDB (a MySQL storage layer for social graph data), ZippyDB (a distributed key-value store), and UP2X (a distributed key-value store for AI/ML services). These characterizations reveal several interesting findings: first, that the distribution of key and value sizes are highly related to the use cases/applications; second, that the accesses to key-value pairs have a good locality and follow certain special patterns; and third, that the collected performance metrics show a strong diurnal pattern in the UDB, but not the other two. We further discover that although the widely used key-value benchmark YCSB provides various workload configurations and key-value pair access distribution models, the YCSB triggered workloads for underlying storage systems are still not close enough to the workloads we collected due to ignorance of key-space localities. To address this issue, we propose amore »key-range based modeling and develop a benchmark that can better emulate the workloads of real-world key-value stores. This benchmark can synthetically generate more precise key-value queries that represent the reads and writes of key-value stores to the underlying storage system.« less
  8. The emergence of Hybrid Shingled Magnetic Recording (H-SMR) allows dynamic conversion of the recording format between Conventional Magnetic Recording (CMR) and SMR on a single disk drive. H-SMR is promising for its ability to manage the performance/capacity trade-off on the disk platters and to adaptively support different application scenarios in large-scale storage systems. However, there is little research on how to efficiently manage data and space in such H-SMR drives. In this paper, we present ZoneAlloy, an elastic data and space management scheme for H-SMR drives, to explore the benefit of using such drives. ZoneAlloy initially allocates CMR space for the application and then gradually converts the disk format from CMR to SMR to create more space for the application. ZoneAlloy controls the overhead of the format conversion on the application I/O with our quantized migration mechanism. When data is stored in an SMR area, ZoneAlloy reduces the SMR update overhead using H-Buffer and Zone-Swap. H-Buffer is a small host-controlled CMR space that absorbs the SMR updates and migrates those updates back to the SMR space in batches to bring down the SMR update cost. Zone-Swap dynamically swaps "hot" data from the SMR space to the CMR space to furthermore »alleviate the SMR update problem. Evaluation results based on MSR-Cambridge traces demonstrate that ZoneAlloy can reduce the average I/O latency and limit the performance degradation of the application I/O during format conversion.« less