Efficient buffering for concurrent disk and tape I/O

Multimedia data poses challenges for efficient storage and retrieval due to its large size and playback timing requirements. For applications that store very large volumes of multimedia data, hierarchical storage offers a scalable and economical alternative to store data on magnetic disks. In a hierarchical storage architecture data is stored on a tape or optical disk based tertiary storage layer with the secondary storage disks serving as a cache or buffer. Due to the need for swapping media on drives, retrieving multimedia data from tertiary storage can potentially result in large delays before playback (startup latency) begins as well as during playback (jitter). In this paper we address the important problem of reducing startup latency and jitter for very large multimedia repositories. We propose that secondary storage should not be used as a cache in the traditional manner — instead, most of the secondary storage should be used to permanently store partial objects. Furthermore, replication is employed at the tertiary storage level to avoid expensive media switching. In particular, we show that by saving the initial segments of documents permanently on secondary storage, and replicating them on tertiary storage, startup latency can be significantly reduced. Since we are effectively reducing the amount of secondary storage available for buffering the data from tertiary storage, an increase in jitter may be expected. However, our results show that the technique also reduces jitter, in contrast to the expected behavior. Our technique exploits the pattern of data access. Advance knowledge of the access pattern is helpful, but not essential. Lack of this information or changes in access patterns are handled through adaptive techniques. Our study addresses both single- and multiple-user scenarios. Our results show that startup latency can be reduced by as much as 75% and jitter practically eliminated through the use of these techniques.

Chapter 6 - Secondary Storage

An archiving model for a hierarchical information storage environment

Tertiary storages, such as tape libraries and optical disc libraries, are becoming the important storage devices in massive data applications. With the massive storage space they have, the tertiary storages have very low access efficiency. Designing good schedule algorithms is an important method to improve the access efficiency in tertiary storage. Stochastic Markov model is used for predicting the expected number of accesses to the data on tertiary storage. Two new schedule algorithms named MarkovMR and MarkovSRF are given also. Generally, in a tape library, there is a robot arm, a few of tape drives and a magazine where a lot of tapes located in. When the tapes are kept in tape drives, we call them online tapes. Otherwise, we call the tapes in the magazine offline tapes. Weight factors are used to above schedule algorithms to favor online tapes so that the requests for online tapes are served first before online tapes are ejected. The weighted algorithms are named wMarkovMR and wMarkovSRF. By compared to the Round-robin policy, the experimental results show that the four schedule algorithms based on Markov model have higher efficiency of data access in tertiary storage. The efficiency of wMarkovMR is highest among all the algorithms. Furthermore, the optimal factors can be derived from experiments.

A database management system can ensure the semantic integrity of a database via an integrity control subsystem. A technique for implementation of such a subsystem is proposed. After a database is updated by transactions, its integrity must be verified by evaluation of a set of semantic integrity assertions. For evaluation of an integrity assertion a number of database pages need to be transferred from the secondary storage to the fast memory. Since certain pages may be required for evaluation of different integrity assertions, the order of the evaluation of the integrity assertions determines the total number of pages fetched from the secondary storage. Hence, the schedule for the evaluation determines the cost of the database verification process. We show that the search for an optimal schedule is an NP-hard problem. Four approximation algorithms that find suboptimal schedules are proposed. They are based on the utilization of intersections among sets of pages required for the evaluation of different integrity assertions. The theoretical worst case behaviors of these algorithms are studied. Finally, the algorithms are compared via a simulation study to a naive, random order verification approach. The methods proposed for minimizing the costs of the batch integrity verification also apply to other problems that can be abstracted to the directed traveling salesman optimization problem. For example, the methods are applicable to multiple to multiple-query optimization and to concurrency control via the predicate locks.

Database Management Systems (DBMS) need to handle large updatable datasets in on-line transaction processing (OLTP) workloads. Most modern DBMS provide snapshots of data in multi-version concurrency control (MVCC) transaction management scheme. Each transaction operates on a snapshot of the database, which is calculated from a set of tuple versions. High parallelism and resource-efficient append-only data placement on secondary storage is enabled. One major issue in indexing tuple versions on modern hardware technologies is the high write amplification for tree-indexes.

Exploring new electrolyte materials is important to comprehend high performance secondary charge storage devices for effective utilization of renewable energy. Ionic liquids with broad electrochemical voltage window and wide range of thermal stability are prospective materials for the same. As an improved version of this class of materials, we report herein, on the synthesis of novel pyrrolidinium based ionic liquid tethered nanoparticle hybrid electrolytes and compared their conductivity and electrochemical cycling behaviors. Hybrid electrolytes are prepared by covalently grafting N-Methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide to the surfaces of pre-synthesized TiO2 nanoparticles at three different core volume fractions, ranging from 0.11 to 0.46. Uniform dispersion of the core nanoparticle within the matrix of the electrolytes improves their mechanical properties. With increasing core volume fractions, the electrical conductivity slightly decreases due to increasing viscosity. Nevertheless, nanoparticle grafting significantly improves the electrochemical performance of the electrolytes. The electrolytes show very good capacitance retentivity (>90%) and long-term cycling stability above room temperature even at the lowest grafting density within symmetric stainless steel electrodes. Impressive room temperature electrochemical performance of these materials within symmetric supercapacitor cell containing CMS graphite as electrodes further demonstrates the applicability of these hybrid materials as promising electrolytes for secondary charge storage devices.

Storage of multimedia data is a critical issue for the overall system's performance and functionality. Multimedia applications must be able to support a variety of data defined as multimedia objects. Multimedia data consist of various objects such as text, image, video and graphics, which need to be synchronized and meet certain timing requirements. The development and evolution of these new applications characterized by high storage needs resulted in strengthening the role and importance of Tertiary Storage Systems. Recent technological advances have resulted in wide availability of commercial products offering near-line, robot-based, tertiary storage libraries. Therefore, such libraries have become an important component of modern large-scale storage servers. The issue of optimal data placement strategies in tertiary storage is considered below. Different configurations of tape libraries and magnetic tape technologies as well as the special attributes of stored data have an impact on the optimal placement.

A massively parallel computer handles a massive amount of data with simultaneous access requests from multiple processors, and therefore it must have a large-capacity secondary storage system of very high concurrency. Such a storage system should consist of many disks that are connected in parallel. With such large-scale parallel disk systems, access load balancing is extremely important in order to enhance the effective operation of all disks. In this paper, we propose a parallel file access method named DECODE (Dynamic Express Changing Of Data Entry) which performs dynamic load balancing over all disks according to the load status of each disk. DECODE can achieve load balancing by changing the disk used for writing data to a low-load disk. The efficiency of this method is verified by preliminary performance evaluation using software simulation under various access conditions, by changing the access pattern and the access size. The effect of some of the parameters used in the method is also evaluated.

10 - Display and Storage Systems

In this modern era of computing, we are surrounded directly or indirectly related to the computer resources and services, and uses several programming language, different database management systems like RDBMS. At the same time, it need respective compilers and editors for different languages and the most important resource is “storage”, which could be either in the form of primary or secondary space storage. Our Industries like banking, health and education are growing with rapid demand of resources. Thus, to reduces the load of resources consumption and improves its capacity with performance, would be major focus into this chapter. This could be crafted with policy-base assignment of resources approach and adaptive self-learning with virtualization of resources for optimization. Using such approaches and methods, it helps in quality of service with higher availability, greater performance, and improved recoverability.

The ever growing needs of large multimedia systems cannot be met by magnetic disks due to their high cost and low storage density. Consequently, cheaper and denser tertiary storage systems are being integrated into the storage hierarchies of these applications. Although tertiary storage is cheaper, the access latency is very high due to the need to load and unload media on the drives. This high latency and the bursty nature of I/O traffic result in the accumulation of I/O requests for tertiary storage. We study the problem of scheduling these requests to improve performance. In particular we address the issues of scheduling across multiple tapes or disks as opposed to most other studies which consider only one or two media. We focus on algorithms that minimize the number of switches and show through simulation that these result in near-optimal schedules. For single drive libraries an efficient algorithm that produces optimal schedules is developed. For multiple drives the problem is shown to be NP-Complete. Efficient and effective heuristics are presented for both single and multiple drives. The scheduling policies developed achieve significant performance gains over naive policies. The algorithms are simple to implement and are not restrictive. The study encompasses all types of storage libraries handling removable media, such as tapes and optical disks.

Reducing the storage space of the relational database management system (DBMS) like Microsoft SQL (MS SQL), MySQL is very challenging nowadays. Using DBMS is vital to any local area network (LAN)-based application including Web-based application and mobile application to store and manage data. These data leave traces on servers and are retained on storage devices for a very long time. Due to heavy program usage and potential user error, the data eventually need to be examined for abnormalities and integrity. The chapter discusses the duplication detection algorithm approaches. In addition, the Levenshtein Algorithm was used and implemented to detect duplicate record in the database alongside the method used for matching records’ multiple fields and the Rule-Based Technique approaches. This topic will contribute knowledge on data cleansing and reducing storage space used by applications and help to maximize storage space of data center.

Improving XML database management system has attracted researchers to consider whether the indexing system is equivalent to a relational database management system. The indexing system is based on labelling the nodes of the XML tree. Different types of labelling scheme have been proposed to label the document quickly and without consuming too much storage space. However, most the studies focused on evaluating the performance of new labelling schemes. The appropriateness of various existing schemes to the particular structure an XML document has not been addressed sufficiently. To investigate this aspect two common XML labelling schemes were employed: Prefix (Dewey Encoding) and Interval (Containment) to label three different examples of XML documents with very different structures. The time and storage space requirements were investigated to compare the relevance of each scheme to the structures of the documents. A number of experiments were conducted and it was found that Dewey Encoding and Containment techniques are relatively fast when labelling shallow tree structures. Dewey required little storage space to save labels of wide tree structures, however, Containment used less storage space when storing the labels of short trees.

We present the design of a log-structured tertiary storage (LTS) system. The advantage of this approach is that it allows the system to hide the details of jukebox robotics and media characteristics behind a uniform, random-access, block-oriented interface. It also allows the system to avoid media mount operations for writes, giving a write performance similar to that of secondary storage.