Multimedia Storage Servers Research Articles

A Flash Translation Layer for nand Flash-Based Multimedia Storage Devices

NAND flash memory-based storage devices are becoming an attractive storage solution for multimedia storage servers because they afford several advantages including fast read access speed and low power consumption. Multimedia storage devices differ significantly from traditional storage devices in that the user files are accessed in a sequential read manner while metadata are updated frequently. In this paper, we propose a new flash translation layer (FTL) scheme called filtering FTL (FFTL) for nand flash-based multimedia storage devices. The main idea of the FFTL scheme is to filter update requests for metadata and manage them separately from requests for user data. Our experimental results show that the proposed FFTL scheme outperforms existing FTL schemes by dramatically reducing the garbage collection overhead.

Disk scheduling on multimedia storage servers

A disk scheduler called MS-EDF is proposed not only to meet the deadlines of all requests, but also to offer the optimal seek time. Through the experiments, the results show our disk scheduling algorithm outperforms the others for multimedia systems in all cases.

A comprehensive analytical performance model for disk devices under random workloads

Our goal is to contribute a common theoretical framework for studying the performance of disk-storage devices. Understanding the performance behavior of these devices will allow prediction of the I/O cost in modern applications. Current disk technologies differ in terms of the fundamental modeling characteristics, which include the magnetic/optical nature, angular and linear velocities, storage capacities, and transfer rates. Angular and linear velocities, storage capacities, and transfer rates are made constant or variable in different existing disk products. Related work in this area has studied Constant Angular Velocity (CAV) magnetic disks and Constant Linear Velocity (CLV) optical disks. We present a comprehensive analytical model, validated through simulations, for the random retrieval performance of disk devices which takes into account all the above-mentioned fundamental characteristics and includes, as special cases, all the known disk-storage devices. Such an analytical model can be used, for example, in the query optimizer of large traditional databases as well as in an admission controller of multimedia storage servers. Besides the known models for magnetic CAV and optical CLV disks, our unifying model is also reducible to a model for a more recent disk technology, called zoned disks, the retrieval performance of which has not been modeled in detail before. The model can also be used to study the performance retrieval of possible future technologies which combine a number of the above characteristics and in environments containing different types of disks (e.g., magnetic-disk-based secondary storage and optical-disk-based tertiary storage). Using our model, we contribute an analysis of the performance behavior of zoned disks and we compare it against that for the traditional CAV disks, as well as against that of some possible/future technologies. This allows us to gain insights into the fundamental performance trade-offs.

File distribution in networks with multimedia storage servers

AbstractIn this paper, we consider a problem in networks with storage servers for providing multimedia service. The design involves assigning communication link capacity, sizing the multimedia servers, and distributing different types of content at each server, while guaranteeing an upper limit on the individual end‐to‐end blocking probability. We consider alternative methods for obtaining the end‐to‐end blocking probability with low computation time and present optimization procedures to obtain an optimal solution. Under a linear cost structure, our numerical investigations consider different scenarios that might be helpful in understanding how to distribute multimedia content for a cost‐optimized solution. © 2001 John Wiley & Sons, Inc.

Disk scheduling in video editing systems

Modern video servers support both video-on-demand and nonlinear editing applications. Video-on-demand servers enable the user to view video clips or movies from a video database, while nonlinear editing systems enable the user to manipulate the content of the video database. Applications such as video and news editing systems require that the underlying storage server be able to concurrently record live broadcast information, modify prerecorded data, and broadcast an authored presentation. A multimedia storage server that efficiently supports such a diverse group of activities constitutes the focus of this study. A novel real-time disk scheduling algorithm is presented that treats both read and write requests in a homogeneous manner in order to ensure that their deadlines are met. Due to real-time demands of movie viewing, read requests have to be fulfilled within certain deadlines; otherwise, they are considered lost. Since the data to be written into disk is stored in main memory buffers, write requests can be postponed until critical read requests are processed. However, write requests still have to be processed within reasonable delays and without the possibility of indefinite postponement. This is due to the physical constraint of the limited size of the main memory write buffers. The new algorithm schedules both read and write requests appropriately, to minimize the amount of disk reads that do not meet their presentation deadlines, and to avoid indefinite postponement and large buffer sizes in the case of disk writes. Simulation results demonstrate that the proposed algorithm offers low violations of read deadlines, reduces waiting time for lower priority disk requests, and improves the throughput of the storage server by enhancing the utilization of available disk bandwidth.

Comparing random data allocation and data striping in multimedia servers

We compare performance of a multimedia storage server based on a random data allocation layout and block replication with traditional data striping techniques. Data striping techniques in multimedia servers are often designed for restricted workloads, e.g. sequential access patterns with CBR (constant bit rate) requirements. On the other hand, a system based on random data allocation can support virtually any type of multimedia application, including VBR (variable bit rate) video or audio, and interactive applications with unpredictable access patterns, such as 3D interactive virtual worlds, interactive scientific visualizations, etc. Surprisingly, our results show that system performance with random data allocation is competitive and sometimes even outperforms traditional data striping techniques, for the workloads for which data striping is designed to work best; i.e. streams with sequential access patterns and CBR requirements. Due to its superiority in supporting general workloads and competitive system performance, we believe that random data allocation will be the scheme of choice for next generation multimedia servers.

Sync classes: a framework for optimal scheduling of requests in multimedia storage servers

There have been many proposals on how media-on-demand servers can effectively allow clients to share resources. In this paper, given a set of clients, we show how these clients may be partitioned into sets of clients who can be serviced through allocation of a single set of resources. As a set of clients may be partitioned into sync-classes in many different ways, we show that a very large class of cost functions may be used to determine which partition to choose. We provide algorithms to compute such optimal splits. Our framework is very generic in the following ways: the system may plug-in any cost function whatsoever, as long as it satisfies four common-sense axioms that evaluate costs; and the system may evaluate the future anticipated requests of a user using any user model (e.g., a Markovian model) that has a specified I/O interface. Thus, a wide variety of predictive methods (of what the user will do) and a wide variety of costing methods may be used within our framework.

Analytical models for mixed workload multimedia storage servers

Efficient resource management is essential in providing scalability in large multimedia information systems serving a variety of applications. In order to explore design tradeoffs in such systems, what is needed are accurate analytical models of mixed workload servers with tractable solutions. Motivated by the need for mixed workload storage servers as well as the need for performance studies of such systems, we first present a family of scheduling algorithm for mixed workload storage servers. We then develop a set of corresponding analytical non-Markovian models. We show how our analytical solution methodology applies to this entire family of models and how it can be used to obtain performance measures of interest for different classes of workloads. Lastly, we illustrate through numerical examples how such models can be used to study performance tradeoffs and facilitate the making of design choices in mixed workload storage servers.

Efficient admission control algorithms for multimedia servers

In this paper, we have proposed efficient admission control algorithms for multimedia storage servers that are providers of variable-bit-rate media streams. The proposed schemes are based on a slicing technique and use aggressive methods for admission control. We have developed two types of admission control schemes: Future-Max (FM) and Interval Estimation (IE). The FM algorithm uses the maximum bandwidth requirement of the future to estimate the bandwidth requirement. The IE algorithm defines a class of admission control schemes that use a combination of the maximum and average bandwidths within each interval to estimate the bandwidth requirement of the interval. The performance evaluations done through simulations show that the server utilization is improved by using the FM and IE algorithms. Furthermore, the quality of service is also improved by using the FM and IE algorithms. Several results depicting the trade-off between the implementation complexity, the desired accuracy, the number of accepted requests, and the quality of service are presented.

Design and evaluation of a multimedia storage server for mixed traffic

The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach.

Merging video streams in a multimedia storage server: complexity and heuristics

Due to recent advances in network, storage and data compression technologies, video-on-demand (VOD) service has become economically feasible. It is a challenging task to design a video storage server that can efficiently service a large number of concurrent requests on demand. One approach to accomplishing this task is to reduce the I/O demand to the VOD server through data- and resource-sharing techniques. One form of data sharing is the stream-merging approach proposed in [5]. In this paper, we formalize a static version of the stream-merging problem, derive an upper bound on the I/O demand of static stream merging, and propose efficient heuristic algorithms for both static and dynamic versions of the stream-merging problem.

Designing a Hierarchical MUltimedia Storage Server

Recent advances in computer storage architectures, high-speed networking technologies and compression techniques support a proliferation of multimedia information dissemination via computer networks. For example, applications such as video-on-demand (VOD) and home shopping services are now possible. A major requirement of VOD application is that the VOD storage server has to store and retrieve a huge amount of video data in a continuous manner. Therefore, near-line storage devices, such as robotic tape libraries, have to be employed in VOD storage servers which can contain thousands of large video objects. In this paper, we study in detail the design issues of a hierarchical multimedia storage server that consists of a disk array for caching and a robotic tape library for the storage of all the video objects. We propose and study in detail the file layout policy in the disk subsystem, the scheduling of the tape subsystem, the video object replacement algorithms, the read/write scheduling of the disk subsystem and the memory buffer requirement.

Scheduling and data layout policies for a near-line multimedia storage architecture

Recent advances in computer technologies have made it feasible to provide multimedia services, such as news distribution and entertainment, via high-bandwidth networks. The storage and retrieval of large multimedia objects (e.g., video) becomes a major design issue of the multimedia information system. While most other works on multimedia storage servers assume an on-line disk storage system, we consider a two-tier storage architecture with a robotic tape library as the vast near-line storage and an on-line disk system as the front-line storage. Magnetic tapes are cheaper, more robust, and have a larger capacity; hence, they are more cost effective for large scale storage systems (e.g., videoon-demand (VOD) systems may store tens of thousands of videos). We study in detail the design issues of the tape sub-system and propose some novel tape-scheduling algorithms which give faster response and require less disk buffer space. We also study the disk-striping policy and the data layout on the tape cartridge in order to fully utilize the throughput of the robotic tape system and to minimize the on-line disk storage space.

Group-guaranteed channel capacity in multimedia storage servers

One of the open questions in the design of multimedia storage servers is in what order to serve incoming requests. Given the capability provided by the disk layout and scheduling algorithms to serve multiple streams simultaneously, improved request scheduling algorithms can reduce customer waiting times. This results in better service and/or lower customer loss. In this paper we define a new class of request scheduling algorithms, called Group-Guaranteed Server Capacity (GGSC), that preassign server channel capacity to groups of objects. We also define a particular formal method for computing the assigned capacities to achieve a given performance objective. We observe that the FCFS policy can provide the precise time of service to incoming customer requests. Under this assumption, we compare the performance of one of the new GGSC algorithms, GGSC W -FCFS, against FCFS and against two other recently proposed scheduling algorithms: Maximum Factored Queue length (MFQ), and the FCFS-n algorithm that preassigns capacity only to each of the n most popular objects. The algorithms are compared for both competitive market and captured audience environments.Key findings of the algorithm comparisons are that: (1) FCFS-n has no advantage over FCFS if FCFS gives time of service guarantees to arriving customers, (2) FCFS and GGSC W -FCFS are superior to MFQ for both competitive and captive audience environments, (3) for competitive servers that are configured for customer loss less than 10%, FCFS is superior to all other algorithms examined in this paper, and (4) for captive audience environments that have objects with variable playback length, GGSC W -FCFS is the most promising of the policies considered in this paper. The conclusions for FCFS-n and MFQ differ from previous work because we focus on competitive environments with customer loss under 10%, we assume FCFS can provide time of service guarantees to all arriving customers, and we consider the distribution of customer waiting time as well as the average waiting time.

Adaptive piggybacking: a novel technique for data sharing in video-on-demand storage servers

Recent technology advances have made multimedia on-demand services, such as home entertainment and home-shopping, important to the consumer market. One of the most challenging aspects of this type of service is providing access either instantaneously or within a small and reasonable latency upon request. We consider improvements in the performance of multimedia storage servers through data sharing between requests for popular objects, assuming that the I/O bandwidth is the critical resource in the system. We discuss a novel approach to data sharing, termed adaptive piggybacking, which can be used to reduce the aggregate I/O demand on the multimedia storage server and thus reduce latency for servicing new requests.

Research issues in multimedia storage servers

Research issues in multimedia storage servers

Scheduling issues in multimedia query optimization

This paper examines the scheduling of concurrent requests on multimedia storage servers consisting of multiple resources, which is a central issue in processing and optimization of complex queries in multimedia database systems [Chaudhuri 1994]. It introduces a formal model for the demands imposed by multimedia requests on the server resources, described a heuristic algorithm for scheduling the requests that is based on the formal model, and presents a formal result that bounds the performance of the schedule produced by the algorithm compared to the optimal schedule. Scheduling requests that involve continuous media data types, for example, audio and video objects, is a challenging problem due to the following distinguishing characteristics of multimedia environments:

Reducing I/O demand in video-on-demand storage servers

Recent technological advances have made multimedia on-demand services, such as home entertainment and home-shopping, important to the consumer market. One of the most challenging aspects of this type of service is providing access either instantaneously or within a small and reasonable latency upon request. In this paper, we discuss a novel approach, termed adaptive piggybacking, which can be used to provide on-demand or nearly-on-demand service and at the same time reduce the I/O demand on the multimedia storage server.

Preemption characterization in Real-Time Multimedia Scheduling

Real-Time Disk-Scheduling policies permit a multimedia storage server to give access to multimedia objects such as text, images, audio and video. In this paper the overhead associated to the context switches caused by two optimal real-time disk-scheduling policies is evaluated and compared. As a result, it is concluded that in general, the SCAN-EDF exhibits less context switches than the SCAN-RM. A new scheduling Algorithm which reduces context switches is presented.

Design of a large scale multimedia storage server

Large scale multimedia storage servers will be an integral part of the emerging distributed multimedia computing infrastructure. However, given the modest rate of improvements in storage transfer rates, designing servers that meet the demands of multimedia applications is a challenging task that needs significant architectural innovation. Our research project, called Massively-parallel And Real-time Storage ( mars) architecture, is aimed at the design and prototype implementation of a large scale multimedia storage server. It uses some of the well-known techniques in parallel I/O, such as data striping and Redundant Arrays of Inexpensive Disks ( raid) and an innovative atm based interconnect inside the server to achieve a scalable architecture that transparently connects storage devices to an atm-based broadband network. The atm interconnect within the server uses a custom asic called ATM Port Interconnect Controller ( apic) currently being developed as a part of an arpa sponsored gigabit local atm testbed. Our architecture relies on innovative data striping and real-time scheduling to allow a large number of guaranteed concurrent accesses, and uses separation of metadata from real data to achieve a direct flow of the media streams between the storage devices and the network. This paper presents our system architecture; one that is scalable in terms of the number of supported users and the throughput.