A Logical Model and Data Placement Strategies for MEMS Storage Devices

MEMS storage devices are new non-volatile secondary storages that have outstanding advantages over magnetic disks. MEMS storage devices, however, are much different from magnetic disks in the structure and access characteristics. They have thousands of heads called probe tips and provide the following two major access facilities: (1) flexibility: freely selecting a set of probe tips for accessing data, (2) parallelism: simultaneously reading and writing data with the set of probe tips selected. Due to these characteristics, it is nontrivial to find data placements that fully utilize the capability of MEMS storage devices. In this paper, we propose a simple logical model called the Region-Sector (RS) model that abstracts major characteristics affecting data retrieval performance, such as flexibility and parallelism, from the physical MEMS storage model. We also suggest heuristic data placement strategies based on the RS model and derive new data placements for relational data and two-dimensional spatial data by using those strategies. Experimental results show that the proposed data placements improve the data retrieval performance by up to 4.0 times for relational data and by up to 4.8 times for two-dimensional spatial data of approximately 320 Mbytes compared with those of existing data placements. Further, these improvements are expected to be more marked as the database size grows.Comment: 37 page

Analyzing the Trimming Activity of Solid-State Drives in Digital Forensics

The primary source for storing digital information has been remained constant for the last two decades, in the form of magnetic disks. However, a sudden shift has taken place in the data storage technology during the recent years where the transistor-based devices are being used as primary storage devices for storing complex data. There are many reasons due to which the manufacturers are shifting their platform from magnetic disks to solid state drives which uses transistor chips and this change is creating problems for the forensic investigators to investigate on the digital evidence. The deleted information can be easily retrieved from the hard disks by following specific guidelines, where as in solid state drives it is almost impossible to retrieve the lost data when TRIM command is enabled. SSDs can sometimes sanitize data all by themselves even if they are not connected to any interface. This paper gives an overview of the hard disks and solid-state drives for data recovery and mainly focuses on the functioning of TRIM command in solid state drives

RAIDX: RAID EXTENDED FOR HETEROGENEOUS ARRAYS

The computer hard drive market has diversified with the establishment of solid state disks (SSDs) as an alternative to magnetic hard disks (HDDs). Each hard drive technology has its advantages: the SSDs are faster than HDDs but the HDDs are cheaper. Our goal is to construct a parallel storage system with HDDs and SSDs such that the parallel system is as fast as the SSDs. Achieving this goal is challenging since the slow HDDs store more data and become bottlenecks, while the SSDs remain idle. RAIDX is a parallel storage system designed for disks of different speeds, capacities and technologies. The RAIDX hardware consists of an array of disks; the RAIDX software consists of data structures and algorithms that allow the disks to be viewed as a single storage unit that has capacity equal to the sum of the capacities of its disks, failure rate lower than the failure rate of its individual disks, and speeds close to that of its faster disks. RAIDX achieves its performance goals with the aid of its novel parallel data organization technique that allows storage data to be moved on the fly without impacting the upper level file system. We show that storage data accesses satisfy the locality of reference principle, whereby only a small fraction of storage data are accessed frequently. RAIDX has a monitoring program that identifies frequently accessed blocks and a migration program that moves frequently accessed blocks to faster disks. The faster disks are caches that store the solo copy of frequently accessed data. Experimental evaluation has shown that a HDD+SSD RAIDX array is as fast as an all-SSD array when the workload shows locality of reference

Atomic Scale Memory at a Silicon Surface

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of 5 atom rows. The writing process involves removal of Si atoms with the tip of a scanning tunneling microscope. The memory can be reformatted by controlled deposition of silicon. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.Comment: 13 pages, 5 figures, accepted by Nanotechnolog

Disk storage management for LHCb based on Data Popularity estimator

This paper presents an algorithm providing recommendations for optimizing the LHCb data storage. The LHCb data storage system is a hybrid system. All datasets are kept as archives on magnetic tapes. The most popular datasets are kept on disks. The algorithm takes the dataset usage history and metadata (size, type, configuration etc.) to generate a recommendation report. This article presents how we use machine learning algorithms to predict future data popularity. Using these predictions it is possible to estimate which datasets should be removed from disk. We use regression algorithms and time series analysis to find the optimal number of replicas for datasets that are kept on disk. Based on the data popularity and the number of replicas optimization, the algorithm minimizes a loss function to find the optimal data distribution. The loss function represents all requirements for data distribution in the data storage system. We demonstrate how our algorithm helps to save disk space and to reduce waiting times for jobs using this data

Incorporating Oracle on-line space management with long-term archival technology

The storage requirements of today's organizations are exploding. As computers continue to escalate in processing power, applications grow in complexity and data files grow in size and in number. As a result, organizations are forced to procure more and more megabytes of storage space. This paper focuses on how to expand the storage capacity of a Very Large Database (VLDB) cost-effectively within a Oracle7 data warehouse system by integrating long term archival storage sub-systems with traditional magnetic media. The Oracle architecture described in this paper was based on an actual proof of concept for a customer looking to store archived data on optical disks yet still have access to this data without user intervention. The customer had a requirement to maintain 10 years worth of data on-line. Data less than a year old still had the potential to be updated thus will reside on conventional magnetic disks. Data older than a year will be considered archived and will be placed on optical disks. The ability to archive data to optical disk and still have access to that data provides the system a means to retain large amounts of data that is readily accessible yet significantly reduces the cost of total system storage. Therefore, the cost benefits of archival storage devices can be incorporated into the Oracle storage medium and I/O subsystem without loosing any of the functionality of transaction processing, yet at the same time providing an organization access to all their data

Influence of different factors on the RAID 0 paired magnetic disk arrays

The rapid technological progress has led to a growing need for more data storage space. The appearance of big data requires larger storage space, faster access and exchange of data as well as data security. RAID (Redundant Array of Independent Disks) technology is one of the most cost-effective ways to satisfy needs for larger storage space, data access and protection. However, the connection of multiple secondary memory devices in RAID 0 aims to improve the secondary memory system in a way to provide greater storage capacity, increase both read data speed and write data speed but it is not fault-tolerant or error-free. This paper provides an analysis of the system for storing the data on the paired arrays of magnetic disks in a RAID 0 formation, with different number of queue entries for overlapped I/O, where queue depth parameter has the value of 1 and 4. The paper presents a range of test results and analysis for RAID 0 series for defined workload characteristics. The tests were carried on in Microsoft Windows Server 2008 R2 Standard operating system, using 2, 3, 4 and 6 paired magnetic disks and controlled by Dell PERC 6/i hardware RAID controller. For the needs of obtaining the measurement results, ATTO Disk Benchmark has been used. The obtained results have been analyzed and compared to the expected behavior

MODELING AND EVALUATION OF A HYBRID OPTICAL AND MAGNETIC DISK STORAGE ARCHITECTURE

A hybrid storage system combining optical disks and magnetic disks is proposed and evaluated via mathematical models. Unlike most current applications of optical disk technology, which consider static databases or deferred update, this research considers environments with a moderate level of near real-time updates. An example of such an environment is databases for administrative decision support systems (DSS). The proposed hybrid storage system uses a write-once, read-many optical disk device (ODD) for the database and a conventional magnetic disk (MD) for storage of a differential file. Periodically, the differential file is used to refresh the ODD file by writing updated records to free space on the ODD. When available free space on the ODD is exhausted, the file is written to new ODD media - - a reorganization operation. Models of storage cost are developed to determine the optimum refresh cycle time, t*, and optimum reorganization cycle time, T*. Parameters of the model include data file volatility, file size, device costs, and costs for refresh and reorganization. Numerical results indicate that the hybrid system is attractive for a broad range of database environments

A Case for Redundant Arrays of Hybrid Disks (RAHD)

Hybrid Hard Disk Drive was originally concepted by Samsung, which incorporates a Flash memory in a magnetic disk. The combined ultra-high-density benefits of magnetic storage and the low-power and fast read access of NAND technology inspires us to construct Redundant Arrays of Hybrid Disks (RAHD) to offer a possible alternative to today’s Redundant Arrays of Independent Disks (RAIDs) and/or Massive Arrays of Idle Disks (MAIDs). We first design an internal management system (including Energy-Efficient Control) for hybrid disks. Three traces collected from real systems as well as a synthetic trace are then used to evaluate the RAHD arrays. The trace-driven experimental results show: in the high speed mode, a RAHD outplays the purely-magnetic-disk-based RAIDs by a factor of 2.4–4; in the energy-efficient mode, a RAHD4/5 can save up to 89% of energy at little performance degradationPeer reviewe

Spin-orbit-coupling induced lateral spin transport from first principles

Everything digital is currently stored in data centres on magnetic hard disk drives which are accessed at will using a magnetic read head. The spinning disks and moving read heads in the hard disks imply slow access time and high-power consumption making data centres giant sponges for electricity. At the same time, semiconductor based storage suffers from thermal dissipation with miniaturization on top of data leakage and high cost. The ideal memory for data storage would be cost-effective, non-volatile, fast and consume less power, combining desirable features of both magnetic and semiconductor storage technology. To this end, the field of “spintronics" promises a new direction towards efficient data storage using magnetic memories. The impetus for the research that has gone into realizing this thesis was fuelled by uncertainties in the reported spin transport parameters and the gap between phenomenological models and experiments in (spin)transport phenomena. The aim of the thesis is to resolve some of the uncertainties by pushing our computational capabilities in investigating microscopic details of transport. Furthermore, I attempt to improve upon existing models of interpretation or prediction used in experiments and application. I studied a number of topics in the field of electronic spin transport in transition metals. Because of their partially filled d-bands and complex Fermi surfaces with spin-orbit coupling, transition metals are rich in spin phenomena that have potential for spintronics applications. Using a density functional theory-based scattering approach, I studied the generation and diffusion of spin currents in non-magnetic 5d and ferromagnetic 3d transition metals. By including thermal disorder, I presented realistic calculations for these metals. I next studied lateral transport in finite size geometries that are encountered in spintronics experiments. This form the last three chapters of the thesis. The main focus of the thesis has been on the determination of the two most important spin-orbit coupling related spin transport properties, the spin flip diffusion length and the spin Hall angle