A Data Migration Scheme Considering Node Reliability for an Autonomous Distributed Storage System

Large-scale storage systems are crucial components in data-intensive applications such as search engine clusters, video-on-demand servers, sensor networks and grid computing. A storage server typically consists of a set of storage devices. In such systems, data layouts may need to be reconfigured over time for load balancing or in the event of system failure/upgrades. It is critical to migrate data to their target locations as quickly as possible to obtain the best performance. Most of the previous results on data migration assume that each storage node can perform only one data transfer at a time. A storage node, however, can typically handle multiple transfers simultaneously and this can reduce the total migration time significantly. Moreover, storage devices tend to have heterogeneous capabilities as devices may be added over time due to storage demand increase. In this paper, we consider the heterogeneous data migration problem, where we assume that each storage node v has different transfer constraint cv, which represents how many simultaneous transfers v can handle. We develop algorithms to minimize the data migration time. We show that it is possible to find an optimal migration schedule when all cvs are even. Furthermore, though the problem is NP-hard in general, we give an efficient algorithm that offers a rigorous (1 + o(1))-approximation guarantee.

The exponentially growing demand for storage puts a huge stress on traditional distributed storage systems. Historically, I/Ops (Inputs/Outputs per second) of hard drives have been the main limitation of storage systems. With the rapid deployment of solid state drives (SSDs) and the expected evolutions of their capacities, price and performance, we claim that CPU and network capacities will become bottlenecks in the future. In this context, we introduce 6Stor, an innovative, software-defined distributed storage system fully integrated with the networking layer. This storage system departs from traditional approaches in two manners: it leverages IPv6 new capabilities to increase the efficiency of its data plane—notably by using directly UDP and TCP rather than HTTP—and thus its performance; and it circumvents scalability limitations of other distributed systems by using a fully distributed metadata layer of indirection to offer flexibility. In this paper, we introduce and describe in details the architecture of 6Stor, with an emphasis on dynamic scalability and robustness to failure. We also present a testbed that we use to evaluate our novel approach by using Ceph—another well known distributed storage system—as baseline. Results obtained on an extensive testbed are presented and some initial conclusions are drawn.

Reliable distributed data storage systems have to employ redundancy codes to tolerate the loss of storages. Many appropriate codes and algorithms can be found in the literature, but efficient schemes for tolerating several storage failures and their embedding in a distributed system are still research issues. In this paper, a variety of redundancy schemes are compared that got implemented in a distributed storage system. All schemes are based on parity and Reed/Solomon and are integrated in the storage system NetRAID. This system allows to configure several user-specified layouts. A performance and reliability analysis of several data and redundancy layouts is presented that combines analytical and experimental results. In a detail, we present performance results for an optimized Reed/Solomon implementation and give an outline for speeding up encoding and recovery by reconfigurable hardware employed in the distributed storage system

Data migration schemes are critical to balance the load in storage clusters for performance improvement. However, as NAND flash based SSDs are widely deployed in storage systems, extending the lifespan of SSD storage clusters becomes a new challenge for data migration. Prior approaches designed for HDD storage clusters, however, are inefficient due to excessive write amplification during data migration, which significantly decrease the lifespan of SSD storage clusters. To overcome this problem, we propose EDM, an endurance aware data migration scheme with careful data placement and movement to minimize the data migrated, so as to limit the worn-out of SSDs while improving the performance. Based on the observation that performance degradation is dominated by the wear speed of an SSD, which is affected by both the storage utilization and the write intensity, two complementary data migration policies are designed to explore the trade-offs among throughput, response time during migration, and lifetime of SSD storage clusters. Moreover, we design an SSD wear model and quantitatively calculate the amount of data migrated as well as the sources and destinations of the migration, so as to reduce the write amplification caused by migration. Results on a real storage cluster using real-world traces show that EDM performs favorably versus existing HDD based migration techniques, reducing cluster-wide aggregate erase count by up to 40%. In the meantime, it improves the performance by 25% on average compared to the baseline system which achieves almost the same effectiveness of performance improvement as previous migration techniques.

Storage devices have evolved to offer increasingly faster read/write access, through flash-based and other solid-state storage technologies. When compared to classical rotating hard disk drives (HDDs), modern solid-state drives (SSDs) have two key differences: (i) the absence of mechanical parts, and (ii) an inherent difference between the process of reading and writing. The former removes a key performance bottleneck, enabling internal device parallelism, whereas the latter manifests as a read/write performance asymmetry. In other words, SSDs can serve multiple concurrent I/Os, and their writes are generally slower than reads; none of which is true for HDDs. Yet, the performance of storage-resident applications is typically modeled by the number of disk accesses performed, inherently assuming symmetric read and write performance and the ability to perform only one I/O at a time, failing to accurately capture the performance of modern storage devices. To address this mismatch, we propose a simple yet expressive storage model, termed Parametric I/O Model (PIO) that captures contemporary devices by parameterizing read/write asymmetry (α) and access concurrency (k). PIO enables device-specific decisions at algorithm design time, rather than as an optimization during deployment and testing, thus ensuring optimal algorithm design by taking into account the properties of each device. We present a benchmarking of several storage devices that shows that α and k vary significantly across devices. Further, we show that using carefully quantified values of α and k for each storage device, we can fully exploit the performance it offers, and we lay the groundwork for asymmetry/concurrency-aware storage-intensive algorithms. We also highlight that the degree of the performance benefit due to concurrent reads or writes depends on the asymmetry of the underlying device. Finally, we summarize our findings as a set of guidelines for designing storage-intensive algorithms and discuss specific examples for better algorithm and system designs as well as runtime tuning.

In tunnel heating systems, phase change materials may minimize the consumption of conventional electric energy, which is very considerate in the field of tunnel heating in cold regions. Because of the phase change material’s poor heat conductivity, its annual growth rate heat absorption and release is slower; thus, the majority of phase change heat storage systems must improve heat transmission. In this study, a spiral metal ring is implanted in the paraffin to improve heat transmission to achieve this objective using a concentric sleeve-type paraffin heat storage device as a medium. Experiments were performed out in order to determine the effects of heating rate, hot fluid flow rate, and the use of a spiral metal ring on the heat storage and release process of a thermal storage device. In comparison to the paraffin thermal storage device, the embedding of the spiral metal ring accelerates the internal thermal performance of the composite heat storage device, resulting in a more uniform temperature distribution. When the thermal radiation heating rate is 60°C, 65°C, or 70°C during the heat storage process, the heat storage time of the composite heating storage device is reduced by 59.2 percent, 44.4 percent, and 40.7 percent, respectively. When the ambient temperature is 26°C and the heat storage device’s starting temperature is 65°C, the exothermic time is reduced by 22.6 percent.

We consider a distributed storage system employing some existing regenerate codes where the storage nodes are scattered in a wireless network. The data collector connects to the storage nodes via orthogonal channels and downloads data symbols from these nodes. In the existing data reconstruction schemes for distributed storage systems, the data collector downloads all symbols from a subset of the storage nodes. Such a full-downloading approach becomes inefficient in wireless networks since due to fading, the wireless channels may not offer sufficient bandwidths for full downloading. Moreover, full-downloading is also less power efficient than partial downloading. In this paper, given a coding scheme employed by the wireless distributed storage system, we propose a partial downloading scheme that allows downloading a portion of the symbols from any storage node. We formulate a cross-layer wireless resource allocation problem for data reconstruction in distributed storage systems employing such partial downloading. To derive the fundamental properties of partial downloading as well as to reduce the complexity of wireless resource allocation, we derive necessary and sufficient conditions for data reconstructability for partial downloading, in terms of the numbers of downloaded symbols from the storage nodes. We also propose channel and power allocation schemes for partial downloading in wireless distributed storage systems. Simulation results are provided to demonstrate the significant power savings by the proposed partial downloading scheme compared to the full-downloading methods for distributed storage.

Behaviors of functional interfaces are crucial factors in the performance and safety of energy storage and conversion devices. Indeed, solid electrode-solid electrolyte interfacial impedance is now considered the main limiting factor in all-solid-state batteries rather than low ionic conductivity of the solid electrolyte. Here, we present a new approach to conducting in situ scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) in order to uncover the unique interfacial phenomena related to lithium ion transport and its corresponding charge transfer. Our approach allowed quantitative spectroscopic characterization of a galvanostatically biased electrochemical system under in situ conditions. Using a LiCoO2/LiPON/Si thin film battery, an unexpected structurally disordered interfacial layer between LiCoO2 cathode and LiPON electrolyte was discovered to be inherent to this interface without cycling. During in situ charging, spectroscopic characterization revealed that this interfacial layer evolved to form highly oxidized Co ions species along with lithium oxide and lithium peroxide species. These findings suggest that the mechanism of interfacial impedance at the LiCoO2/LiPON interface is caused by chemical changes rather than space charge effects. Insights gained from this technique will shed light on important challenges of interfaces in all-solid-state energy storage and conversion systems and facilitate improved engineering of devices operated far from equilibrium.

The exploitation of renewable wind and solar energy for sustainable development is an important part of national and international energy policies. Due to the variability of wind and solar power, energy storage systems allowing effective management of power generation are required. Nowadays there are several technologies that are considered for energy storage. The production of hydrogen by water electrolysis is now considered one of the most promising technologies. Ammonia is considered as a potential hydrogen carrier, while the NH3 electrosynthesis from N2 and H2O looks attractive currently limited by its low efficiency. Electrochemical CO2 reduction another attractive technology to production of liquid fuels. All these technologies require efficient and cheap electrocatalysts for successful industrial implementation. The emergence of new multifunctional materials continuously increases the expectations for the performance of energy conversion and storage devices. MXenes, a family of two-dimensional transition metal carbides has been discovered as candidate for these applications [1], [2]. MXene/metal composites are considered as promising electrocatalysts for several processes. Ni and Ni-based alloy (Ni-Cu) electrodes have been employed as non-precious metal catalysts for hydrogen production owing to their substantial catalytic activity in hydrogen evolution reaction (HER) in alkaline media. However, in economical water-alkali electrolysers, the sluggish water dissociation kinetics (Volmer step) in platinum-free electrocatalysts results in poor hydrogen-production activity. MXene/nano-metal composites as electrocatalysts for hydrogen evolution reaction (HER) in an alkaline medium, demonstrate lower overpotential compared to balk metal electrode at high current densities. An enhanced catalytic activity of MXene/nano-metal composite attributed to the acceleration of the Volmer stage in HER process in alkaline media, by enhancing the water adsorption and dissociation on the catalyst surface where water dissociation is a rate-limiting step. This work proposes a concept of composite structures composed of MAX phase/metal-Al alloy and MXene/metal as functional materials. The concept is based on the combination of the initial MAX phase with metal alloys (Ni, Cu), tuning MAX phase and metal-Al alloy ratio, carbon content and synthesis conditions, followed by Al etching.In more details this work explores the possibilities for the processing of Ni-Al/MAX phase or Cu-Al/MAX phase and corresponding Ni/MXene or Cu/MXene - containing composite electrodes for energy conversion and storage application. Synthesis of powder mixtures with extra Ni or Cu and Al content (e.g. Cu:Ti:Al:C = 1:2:4.5:2) resulted in products containing modified titanium-based MAX phase material and Ni-Al or Cu-Al alloys [2]. It was found that the presence of Cu and Al excess in the reaction mixture promotes the formation process of conventional MAX phases (Ti3AlC2) due to generating Al-rich metal-Al alloys with a lower melting point. Further etching of these sintered products (Ni-Al or Cu-Al/ MAX phase) in HF or alkaline solution allowed the direct formation of electrodes with active surface containing MXene and nanoporous metal (Cu, Ni) composites [2, 3] with a well-developed 3D porous MXene/metal structure possessing good mechanical integrity, electrical conductivity and catalytic activity in hydrogen evolution reaction [2, 3].

This paper analyzes the problems of load balance caused by data access in parallel file systems and gives an accurate way to estimate the load of Data Servers. On the base of this evaluation, the paper proposes an adaptive loading data migration (ALDM) strategy to balance the load of data servers. Experiment results show ALDM has little impact on system performance during data migration, and the performance improves about 10% after data migration completed. Furthermore, ALDM also has good adaptability to various loads in different storage systems.

Transition metal carbides, nitrides, and carbonitrides (MXenes) have become an appealing framework for developing various energy applications. MXenes with van der Waals (vdW) interactions are facile, highly efficient, affordable, and self-assembled features that improve energy density. MXenes exhibit large surface area, high electric conductivity, and excellent electrochemical characteristics for various energy applications. This review summarizes and emphasizes the current developments in MXene with improved performance for energy storage or conversion devices, including supercapacitors (SCs), various types of rechargeable batteries (RBs), solar cells, and fuel cells. We discuss the crystal structures of MXenes properties of MXenes and briefly discuss them for different types of energy applications. Finally, the critical outlook and perspective for the MXene progress for applications in energy applications are also described.

To satisfy more and more complicated requirements on information recording, processing, exchange etc. in newly developed intelligent satellites, a distributed storage system is designed based on SpaceWire network in satellite platform. In this distributed storage system, a SpaceWire router unit serving as the core device of star network connects several nodes, including onboard computers, namely, satellite management unit (SMU), data interface units (DIU) and other nodes like attitude and orbit sensors, space environment monitor instruments and payload controllers, etc. A certain number of standard flash memory modules are separately incorporated into SMU and DIUs to provide comprehensive data recording and exchange service for all nodes in the network. All memory modules are centrally controlled by SMU software to store authorized data in specific type files and retrieve data according to policies set by remote memory access protocol commands. Memory modules that can run in parallel in the distributed storage system produce very high data throughput, which boosts satellite platform capability to a great extent. Backup mechanism among memory modules is deployed and any module can be replaced by others when it meets failure, this makes the storage system robust and reliable. Testing and verification work performed on the distributed storage system shows that the system works quite well and also reveals its attractive effect on improving satellite platform efficiency.

Exploring low-cost and high-efficient electrocatalyst is an exigent task in developing novel sustainable energy conversion systems, such as fuel cells and electrocatalytic fuel generations. 2D materials, specifically 2D superlattice materials focused here, featured highly accessible active areas, high density of active sites, and high compatibility with property-complementary materials to form heterostructures with desired synergetic effects, have demonstrated to be promising electrocatalysts for boosting the performance of sustainable energy conversion and storage devices. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the 2D superlattice-based catalysts yet remain ambiguous. In this review, based on the recent progress of 2D superlattice materials in electrocatalysis applications, the rational design and fabrication of 2D superlattices are first summarized and the application of 2D superlattices in electrocatalysis is then specifically discussed. Finally, perspectives on the current challenges and the strategies for the future design of 2D superlattice materials are outlined. This review attempts to establish an intrinsic correlation between the 2D superlattice heterostructures and the catalytic properties, so as to provide some insights into developing high-performance electrocatalysts for next-generation sustainable energy conversion and storage.

Distribution network is one of the essential part of the power system always suffers from overload condition and voltage fluctuations, which reduces its efficiency. To overcome this problem addition of the renewable energy sources is preferred. Adding of energy storage devices is essential, due to the intermittent nature of renewable energy sources. Hence the combination of renewable and energy storage devices will play a vital role in enhancing the power transfer capability of Distribution network and power system stability. This paper deals with the characteristics, performance and comparisons of various storage devices.

The depletion of traditional fossil energy and the air pollution caused by the burning of fossil fuels have forced science authors from all over the world to gradually turn their attention to the development and utilization of renewable energy. However, limited by the defects of less exposed active surface and slow diffusion of traditional materials, nanomaterials have advantages that traditional materials cannot match and can significantly improve the performance of energy conversion and storage devices. Based on this, this paper studies the application and economic benefits of nanomaterials in the field of new energy and environment and provides a new idea for the development direction of nanomaterials in the field of new energy and environment. This article selects three different survey objects to correctly measure the energy consumed by the three groups of experimental vehicles traveling 1 km, 5 km, 10 km, and 20 km and the content of substances that pollute the environment. At the same time, the three traditional electrodes are connected. The electrochemical workstation of the system measures the electrochemical performance of nanomaterials to analyze the application of nanomaterials in the field of new energy and environment and the economic benefits brought by them. The experiment proves that AgPdMo/MoS2 NWs has the smallest charge transfer resistance of 259.3 Ω, the smallest impedance, and the fastest electron transfer rate. The charge transfer resistances of MoS2 NSs, AgPd NWs, and AgPdMo NWs are 37079 Ω, 398.4 Ω, and 916.6 Ω.