A.L. Narasimha Reddy and James C. Wyllie. I/o issues in a multimedia system. IEEE Computer, 27(3):69-- 74, 1994.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to the client. Specifically, with T denoting the round length, within each round and for every stream, the server retrieves a block of video of bT bytes from the disk subsystem and sends to the network bT bytes. We assume that each disk in the disk array uses the SCAN scheduling algorithm [7]. Specifically, within each round, each disk arm sweeps across its entire platter exactly once with no back tracking. Because we assume the SCAN scheduling algorithm, the overhead incurred within a round for a given disk has the following form disk overhead = seek rot, where I is the number ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69-74, March 1994.

....disk in the proxy s disk array consists of single platter side and a single arm. We assume that the proxy server retrieves data for the ongoing video streams in constant time rounds; we denote the round length by T. We also assume that each disk in the disk array uses the SCAN scheduling algorithm [20]. Specifically, in each round, each disk arm sweeps across its entire platter exactly once with no back tracking. With the SCAN scheduling algorithm, the overhead incurred within a round for a given disk is disk overhead = seek q Ilrot, where I is the number of streams that the disk is ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69 74, March 1994.

....parameter) different accuracies of advance knowledge, and different service requirements. Storage systems for continuous media, and the associated bandwidth and latency guarantees, make heavy use of scheduling to maximize storage eiticiency while providing as much predictability as possible [4, 56]. Network resource scheduling theory may be helpful for advances in storage management, as there are several parallels: In networking terms, advance knowledge of an access pattern is a transfer specification, each storage device and requesting application is a source or destination, and the cache ....

REDDY, A. N., AND WYLLIE, J. C. I/O issues in a multimedia system. IEEE Computer (March 1994).

....[2] Therefore we need to control the burstiness of server transmisity queues: q 0 (high priority) is assigned for stream type sions. traffic, and q 1 (low priority) is assigned for web traffic. The traffic shaper is depicted in Fig. 3. There are M send As our disk is scheduled using C SCAN 2 [10] within the queues in the traffic shaper. Each send queue serves one operating system, we have chosen a maximum concurrency (web or CM) data block at a time. Assume that m out of of MD 5 10 to minimize disk seek overhead. To allocate the M send queues are active, that is, have data blocks for 60 ....

A. L. N. Reddy and J. C. Wyllie, I/O issues in a multimedia system, IEEE Comput. 27(3), 1994, 69--74.

....in the proxy s disk array consists of single platter side and a single arm. We assume that the proxy server retrieves data for the ongoing video streams in constant time rounds; we denote the round length by T . We also assume that each disk in the disk array uses the SCAN scheduling algorithm [20]. Speci cally, in each round, each disk arm sweeps across its entire platter exactly once with no back tracking. With the SCAN scheduling algorithm, the overhead incurred within a round for a given disk is disk overhead = l seek Il rot ; where I is the number of streams that the disk is ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69-74, March 1994.

....for different QoS and server parameters. Section 5 summarizes our contributions. 1 There have been a number of different approaches for storage and retrieval of real time video data. Disk head scheduling algorithms for real time multimedia scheduling of single disk systems were analyzed in [14, 15]. Non contiguous disk allocation of streams was proposed and admission control based on constrained layout designs were analyzed in [12] A disk head scheduling algorithm, group sweeping scheme with the objective of minimizing buffer space and access time was presented in [20] For the SPIFFI ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a Multimedia System. Computer, 27(3):69--74, March 1994.

....such as content loading require Tiger Shark to perform non realtime I O to the file system while real time streams are being played and recorded. Tiger Shark allows all disksystem bandwidth not consumed by real time streams to be used for non realtime I O in a manner similar to that described in [9]. During file system operation, Tiger Shark keeps track of the fraction s of this bandwidth actually used by currently playing streams. After executing a non realtime I O taking time t, Tiger Shark waits for time t(1 s) s before starting the next non realtime I O. Tiger Shark uses an EDF ....

Narasimha Reddy and James C. Wyllie, I/O issues in a multimedia system, IEEE Computer, 27(3):69-74, 1994.

....inter stream temporal relationships are defined, and an approach to maintaining synchronization among streams is outlined. Finally, the authors devise an algorithm for maintaining stream storage parameters during editing operations. 6.3. 6 Layout and retrieval scheduling Reddy and Wyllie [59] propose a disk scheduling policy designed to support aperiodic requests with low delay requirements (such as those of CLSA applications) under a heavy concurrent workload of periodic real time requests. The intuition is that SCAN disk retrieval scheduling works well for minimizing disk seek time, ....

....systems, showing the maximum number of admissible users as a function of segment size for a given buffer capacity, startup latency, or aggregate disk bandwidth constraint. Although SCAN disk scheduling under random block placement is known to perform well with respect to maximizing disk bandwidth [59, 72], the undesirable effects are potentially large startup latency and server buffer requirements. Assume that in each round, at least a round s worth of data is retrieved for each stream. Intuitively, under SCAN each stream must wait until the end of the round to begin playback, since the next block ....

A. L. Narasimha Reddy and James C. Wyllie. I/O issues in a multimedia system. IEEE Computer, pages 69--74, March 1994.

.... depends on the network and client (Anderson et al. 1992) A less formal approach to resource reservation and scheduling based on heuristics is presented by Garofalakis and Ioannidis (1995) Much work on resource reservation in multimedia servers deals with disk scheduling (Reddy and Wyllie 1993; Reddy and Wyllie 1994; Mourad 1996) Concentrating on the system bus instead, Khayat and Bovopoulos (1994; 1995) develop a scheduling algorithm for real time continuous data traffic. However, their approach is restricted to packetised system buses, which are rarely used in conventional architectures. Resource ....

Reddy, A. L. N and J. C Wyllie, 1994. I/O Issues in a Multimedia System. IEEE Computer 27(3):69--74.

....VCR with play, pause and rewind operations [Jardetzky92] implying that demands for I O bandwidth are constant for prolonged periods of time. With these simplified file access patterns it is possible to provide stream oriented I O at a predetermined rate purely by use of large amounts of read ahead [Reddy94]. Unfortunately this abstraction is completely unsuited to conventional generalpurpose file access. Random access to files is usually very slow and often not allowed at all. Where it is allowed, it often causes transient QoS problems for other streams. In a multimedia file system, disk layout is ....

A. L. Narashima Reddy and James C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, pages 69--74, March 1994. (p 97)

....and costs through a case study. 2 Scheme Sweep In this section we briefly describe a well known multimedia delivery scheme, which we call Sweep. Scheme Sweep uses an elevator policy for disk scheduling in order to amortize disk seek overhead. It is representative of a class of schemes [4, 9, 10, 12] that optimize throughput by reducing disk seek overhead. Studies [10] show that an elevator policy is superior for retrieving continuous media data in comparison to a policy in which requests with the earliest deadlines are serviced first. We will use scheme Sweep as a benchmark for comparing ....

....describe a well known multimedia delivery scheme, which we call Sweep. Scheme Sweep uses an elevator policy for disk scheduling in order to amortize disk seek overhead. It is representative of a class of schemes [4, 9, 10, 12] that optimize throughput by reducing disk seek overhead. Studies [10] show that an elevator policy is superior for retrieving continuous media data in comparison to a policy in which requests with the earliest deadlines are serviced first. We will use scheme Sweep as a benchmark for comparing with other schemes. For now, let us assume a single disk and let us make ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. Computer, 2:69--74, March 1994.

....guarantees. We present a framework for real time parallel I O. In Section 2, we present our parallel I O model. A real time, parallel disk scheduling algorithm RT OPT that maximizes the number of clients that can be supported, is presented in Section 3. For any fixed disk head scheduling policy [6], we show that RT OPT is optimal in that if in its schedule, any block misses its deadline then there does not exist any schedule in which all blocks can meet their deadlines. In Section 4 we present simulation results for RT OPT using traces of MPEG video streams, by empirically determining the ....

....video streams, by empirically determining the number of clients that can be supported for different QoS and server parameters. There have been a number of different approaches for storage and retrieval of real time video data. Disk head scheduling and single disk data placement were addressed in [6, 8]. For the SPIFFI video server, 3] proposed a real time priority based disk scheduling algorithm that partitions requests into priority classes based on the nearness of their deadlines. In [1, 2] admission and resource allocation algorithms for VBR CDL video streams were studied in a singledisk ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a Multimedia System. Computer, 27(3):69--74, 1994.

....requirements do not exceed the total amount of available resources. This approach accepts more users than the pessimistic approach, but QoS can be violated in some situations. Scheduling algorithms play an important role in VOD systems, where concurrent streams need to be read effectively [13, 14, 15, 19]. The simplest method is Round Robin (RR) In RR scheduling, the streams are serviced in the same order in each service cycle(period) It appears fair, needs little overhead in scheduling, and needs less buffer space than other methods [5] However, the disk head is required to move in a random ....

.... [1] A third algorithm, SCAN, operates by scanning 3 the disk head back and forth across the surface of the disk, retrieving a requested block as the head passes over it [6] One variant of this basic algorithm combines SCAN with EDF, and is referred to as the SCAN EDF scheduling algorithm [15]. In SCAN EDF scheduling, the requests with the earliest deadlines are served first, but if several requests have the same deadline or deadlines lying closely together, then their respective blocks are accessed using the SCAN algorithm. Clearly, the effectiveness of the SCAN EDF technique is ....

A.L.N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69-- 74, March 1994. 18

....instant a read is initiated for it (which depends upon the schedule) till it its deadline. There have been a number of different approaches for storage and retrieval of realtime video data. Disk head scheduling algorithms for real time multimedia scheduling of single disk systems were analyzed in [40, 41]. Non contiguous disk allocation of streams was proposed and admission control based on constrained layout designs were analyzed in [37] A disk head scheduling algorithm, group sweeping scheme with the objective of minimizing buffer space and access time was presented in [47] For the SPIFFI ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69--74, March 1994.

....does not vary from one period to another. However, the major drawback of RR scheduling is that it does not exploit the relative positions of the media blocks being retrieved during a period [12, 1] To address the limitations of the RR scheduling algorithm, the SCAN disk algorithm has been adapted [14]. Notice that in the case of the RR algorithm, since the order in which clients are serviced is fixed across periods, the maximum separation between the retrieval times of successive requests of a client is limited by the duration of a period. However, in the case of SCAN, the relative order for ....

....requirements do not exceed the total amount of available resources. This approach accepts more users than the pessimistic approach, but QoS can be violated in some situations. Scheduling algorithms play an important role in VOD systems, where concurrent streams need to be read effectively [13, 11, 18, 14]. The simplest method is Round Robin (RR) In RR scheduling, the streams are serviced in the same order in each service cycle(period) It appears fair, needs little overhead in scheduling, and needs less buffer space than other methods. However, the disk head is required to move in a random ....

[Article contains additional citation context not shown here]

A.L.N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69-- 74, March 1994.

....media. Ghandeharizadeh and Ramos [3] have tackled the problem of maximizing retrieval bandwidth by striping continuous data across several disks in a round robin fashion. This enables the system to utilize the aggregate bandwidth of those disks to retrieve an object in real time. Reddy and Willy [10] have proposed a hybrid disk arm scheduling called Scan EDF. Jadav et al. 5] have proposed a logical model of a multimedia on demand server which exploits data access patterns to maximize the number of simultaneous streams served. To a very large extent, most of these proposals aim to minimize ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. IEEE Computer, pages 69--74, Mar. 1994.

....model of a cluster is appropriate for a set of terminals connected to a group of processors, it is unsuited for geographically separated clients that do not possess information about server internals. A large amount of research has focused on special purpose servers for continuous media data [18, 48, 49, 99, 118, 119, 128]. The Fellini system is a single server machine with multi disks with buffer management techniques for continuous media along with text data types [90] Berson et al. also evaluate multi disk architectures using staggered striping schemes to effectively utilize disk bandwidth and also handle ....

N. A.L. Reddy and J. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, 27(3):69 -- 74, March 1994.

.... desirable to reduce buffer requirements in the case of high bit rated objects [3] 6] There are two classes of disk scheduling algorithms for CM servers, non round based algorithms and round based algorithms [5] In non round based algorithms, including Earliest Deadline First(EDF) and SCAN EDF [8], each object is serviced independently with the potential to utilize its optimal cycle length. 7] explains how to merge different patterns of media strands. In contrast, under the round based model, all streams are serviced once in a fixed round. In other words, they are serviced using a single ....

A.L.N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69--74, March 1994.

....and buffer management, network bandwidth is assumed to be sufficient. Usually, The Video server reads data from the disk in cycles of a fixed length in time, called a round. A certain amount of data, enough to be played for the round is retrieved from the disk in a round and sent over the network [9][10] Thus the blocks of the video objects have the same playback time as a round. It is called the CTL (Constant Time Length) method, and it is shown to outperform CDL (Constant data Length) for predominantly read only environment like VOD systems. All the notation in this paper is defined in ....

A.L. Narasimha Reddy and James C. Wyllie. I/O issues in a multimedia system. IEEE Computer, 27(3), pages 67-74, March 1994.

....et al. 98] Garcia Martinez et al. 2000] # EDF strategy [Liu et al. 73] serves the block request with the nearest deadline first. Strict EDF may cause low throughput and very high seek times. Thus, EDF is often adapted or combined with other disk scheduling strategies. # SCAN EDF strategy [Reddy et al. 94] combines the seek optimization of SCAN and the real time guarantees of EDF. Requests are served according to their deadline. The request with the earliest deadline is served first like in EDF. If multiple requests have the same (or similar) deadline, SCAN is used to define the order to handle ....

....scheduling. However, there has only been done little work on disk scheduling algorithms for mixed multimedia data workloads, serving discrete and continuous multimedia data requests at the same time. Some examples are described in [Rompogiannakis et al. 98] Lin et al. 91] Nerjes et al. 98] Reddy et al. 94] Ramakrishnan et al. 93] and [Wijayaratne et al. 99] These algorithms have to satisfy three performance goals: 1) display continuous media streams with minimal delay jitter; 2) serve discrete requests with small average response times; and (3) avoid starvation of discrete request and keep ....

Reddy, A.L.N., Wyllie, J.C.: I/O Issues in a Multimedia System, IEEE Computer, Vol. 27, No. 3, March 1994, pp. 69-74 T. Plagemann, V. Goebel, P. Halvorsen, O. Anshus 25

....Section 12 offers our conclusions. 2 Scheme Sweep In this section we briefly describe a well known media data delivery scheme, which we call Sweep. Scheme Sweep uses an elevator policy for disk scheduling in order to amortize disk seek overhead. It is representative of a class of schemes [11, 14, 19, 21, 24] that improve throughput by reducing disk seek overhead. Reddy and Wylie [21] show that an elevator policy is superior for retrieving continuous media data in comparison to a policy in which requests with the earliest deadlines are serviced first. We will use scheme Sweep as a benchmark for ....

....a well known media data delivery scheme, which we call Sweep. Scheme Sweep uses an elevator policy for disk scheduling in order to amortize disk seek overhead. It is representative of a class of schemes [11, 14, 19, 21, 24] that improve throughput by reducing disk seek overhead. Reddy and Wylie [21] show that an elevator policy is superior for retrieving continuous media data in comparison to a policy in which requests with the earliest deadlines are serviced first. We will use scheme Sweep as a benchmark for comparing with other schemes. During a sweep of the disk, Sweep reads one segment ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. Computer, 2:69--74, March 1994.

....to the client. Specifically, with T denoting the round length, within each round and for every stream, the server retrieves a block of video of bT bytes from the disk subsystem and sends to the network bT bytes. We assume that each disk in the disk array uses the SCAN scheduling algorithm [7]. Specifically, within each round, each disk arm sweeps across its entire platter exactly once with no back tracking. Because we assume the SCAN scheduling algorithm, the overhead incurred within a round for a given disk has the following form disk overhead = l seek Il rot ; where I is the ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69--74, March 1994.

....allocation algorithm is presented which optimizes the buffer requirement of a video on demand system; however, the issue of buffer replacement is not considered. A number of other schemes for handling the storage and retrieval of continuous media data from disk have been proposed in the literature [1, 6, 3, 7, 2]. Among the existing work, only [1, 7] address the issue of servicing non real time requests concurrently with real time requests. Also the schemes presented in [1, 6] do not attempt to reduce disk latency. Finally, none of the schemes discuss buffer page replacement policies for continous media ....

....the buffer requirement of a video on demand system; however, the issue of buffer replacement is not considered. A number of other schemes for handling the storage and retrieval of continuous media data from disk have been proposed in the literature [1, 6, 3, 7, 2] Among the existing work, only [1, 7] address the issue of servicing non real time requests concurrently with real time requests. Also the schemes presented in [1, 6] do not attempt to reduce disk latency. Finally, none of the schemes discuss buffer page replacement policies for continous media servers. The remainder of the chapter ....

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69--74, March 1994.

....to completion of the display of the first block of X, the system stages the next block of X in memory to support a hiccup free display. Since RD RC , the bandwidth of the disk can be multiplexed to support several simultaneous displays. Variations of this simple technique have been described in [Pol91, CP93, RV93, TPBG93, RW94, BGMJ94]. In addition to ensuring a continuous display, a system designer must consider the performance requirements of an application. In an ideal environment, a system costs zero dollars, serves an infinite number of displays with each display observing a zero startup latency time. However, such a ....

A. L. N. Reddy and J. C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer Magazine, 27(3):69--74, March 1994.

....for Continuous Data Requests The SCAN algorithm is inapplicable for continuous data requests since it is oblivious of deadlines. The Earliest Deadline First (EDF) algorithm [11] is a natural choice; however, it has poor performance since it does not attempt to reduce the overhead. SCAN EDF [17] is a hybrid that serves requests in EDF order, but when several requests have the same deadline, they are served using SCAN. Most related recent research has adopted the notion of scheduling with rounds [1, 6, 7, 15, 20] Each continuous data object (stream) is divided into blocks (also called ....

....blocks in a group. Thus, when there is only one group GSS reduces to SCAN and when each stream is in its own group GSS reduces to round robin. 1.1. 3 Disk Scheduling Algorithms for Mixed Media Workloads To our knowledge, the only works with some relevance to mixed media disk scheduling are [17, 10, 12, 13, 14]. The work in [17] overviewed the performance goals for mixed workload scheduling, which are similar to ours, and studied only how some known algorithms for continuous request scheduling, such as EDF and SCAN EDF, affect the response time of discrete (or aperiodic, as they call them) requests. A ....

[Article contains additional citation context not shown here]

A.L.N. Reddy and J.C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, March 1994, pp. 69-74.

....rates. For example, a Seagate ST31200W disk consists of 23 zones with bandwidths varying from 2.33 to 4.17 megabytes per second (MB s) see Table 1b. A number of studies have investigated techniques to support a hiccup free display of continuous media, video and audio, using magnetic disk drives [AH91, RVR92, RV93, VR93, CL93, TPBG93, RW94a, YCK93, Gem93]. These studies assume a fixed transfer rate for a disk drive. If a system designer elects to use one of these techniques, the system is forced to use the minimum transfer rate of the zones for the entire disk in order to guarantee a continuous display of video objects. We term these studies ....

A. L. N. Reddy and J. C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer Magazine, 27(3):69--74, March 1994.

....striping. Our conclusion and future research directions are contained in Section 5. 2 Related Work The physical design of a storage manager that can support continuous media data types has also been investigated in several earlier studies, including [AH91, RVR92, RV93, VR93, CL93, TPBG93, RW94, YCK93, Gem93] All of these studies assume that the bandwidth required to display an object is lower than the bandwidth of a single disk drive. Several studies investigate either disk scheduling [RW94, TPBG93] or the placement of data across the surface of a disk drive [CL93, RV93] to enhance ....

....been investigated in several earlier studies, including [AH91, RVR92, RV93, VR93, CL93, TPBG93, RW94, YCK93, Gem93] All of these studies assume that the bandwidth required to display an object is lower than the bandwidth of a single disk drive. Several studies investigate either disk scheduling [RW94, TPBG93] or the placement of data across the surface of a disk drive [CL93, RV93] to enhance the performance of the disk subsystem. TPBG93, VR93, YCK93] all deal with a RAID [Pat93] as its target hardware platform, the remaining studies assume an architecture that consists of a single disk ....

A. L. N. Reddy and J. C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer Magazine, 27(3):69--74, March 1994.

....locations of the data so that these I O requests can all be serviced when the disk head sweeps unidirectionally (inward or outward) across the disk surface. Though the idea is quite simple, the Scan policy has been gaining more attention than before due to emerging of multimedia storage systems[3, 6, 7]. In the design of multimedia storage systems, an essential issue is how to guarantee uninterrupted delivery of continuous data. This means that the systems must meet certain real time requirements. Without a tight upper bound based on an accurate disk seek time model, the designers of multimedia ....

NARASIMHA REDDY, A.L., AND WYLLIE, J.C. I/O issues in a multimedia system. IEEE Computer 27, 3 (Mar 1994), pp. 69--74.

....array structure to derive the optimal configuration for specific requirements. Key terms: multimedia, storage system, on demand playback, disk bandwidth, disk array 1 Introduction In recent years, the design of mass storage systems for multimedia applications has become an active research topic [1, 2, 3, 4, 5, 6, 7]. One of the most This research was sponsored in part by the National Science Council of R.O.C. under grant NSC 83 0408 E 002 002. important applications of multimedia storage systems is on demand playback of video or high quality audio programs [5, 6, 8, 9, 10, 11, 12, 13, 14] In on demand ....

A.L. Narasimha Reddy and James C. Wyllie. I/O issues in a multimedia system. IEEE Computer, Vol.27, No.3, March 1994.

....to that of a VCR with play, pause and rewind operations [15] implying that demands for I O bandwidth are constant for prolonged periods of time. With these simplified access patterns it is possible to provide stream oriented I O at a predetermined rate purely by use of large amounts of read ahead [16]. Unfortunately, this abstraction is completely unsuited to conventional general purpose file access. Random access to files is usually very slow and often not allowed at all. Where it is allowed, it often causes transient QoS problems for other streams. 5 Custom Storage Systems There are a ....

A. L. Narashima Reddy and James C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, pages 69--74, March 1994.

....disk queues and send new operations to disks whenever they are ready to service new requests. They can implement disk queue scheduling policies to optimize disk I O queue time (e.g. SCAN, C SCAN, LOOK, C LOOK [11, 25] or guarantee real time delivery of data through algorithms such as scan EDF [18]. Currently, only one disk driver exists. This driver implements a combined read write queue and schedules I O requests through the C LOOK scheduling policy. It uses a Unix file (ordinary file, or raw device) as back end. 4 Patsy Patsy is the instantiation of the cut and paste library to a ....

A. L. Narasimha Reddy and James C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, pages 69--74, March 1994.

....control algorithm using dynamic period is proposed in section 4 and our simulation results are presented in section 5. Finally, our conclusions are given in section 6. 2 Related Work Scheduling algorithms play an important role in VOD systems, where concurrent streams need to be read effectively [7, 10, 8]. Several combinations of conventional disk scheduling algorithms and real time scheduling techniques have been investigated in the recent past. The simplest of all such techniques is the round robin (RR) scheduling algorithm, in which the order in which clients are serviced does not vary from one ....

....does not vary from one period to another. However, the major drawback of RR scheduling is that it does not exploit the relative positions of the media blocks being retrieved during a period [2] To address the limitations of the RR scheduling algorithm, the SCAN disk algorithm has been adapted [8]. Notice that in the case of the RR algorithm, since the order in which clients are serviced is fixed across periods, the maximum separation between the retrieval times of successive requests of a client is limited by the duration of a period. However, in the case of SCAN, the relative order for ....

[Article contains additional citation context not shown here]

A.L.N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69-- 74, March 1994.

....mostly focus on data layout and retrieval and delivery techniques which facilitate maintaining of continuity in data delivery while providing either deterministic or statistical QoS guarantees. Scheduling of mixed workloads has not received as much attention. Although it was briefly mentioned in [15], a more detailed (and to our knowledge first) study was presented in [10, 11, 13] where the authors discuss a stochastic approach to QoS provisions to both types of workloads as well as present (somewhat coarse) analytical models for computing the performance measures of interest. This is the ....

A.L.N. Reddy and J. Wyllie. I/O Issues in a Multimedia System. IEEE Computer, 27(3):69-- 74, March, 1994.

....may limit the throughput of the system. We intend to construct simulation models to investigate the alternative schemes further. 8 Related Work The physical design of a storage manager that can support continuous media data types has been investigated in several earlier studies, including [AH91, RVR92, RV93, CL93, TPBG93, RW94]. All studies assume that the bandwidth required to display an object is lower than the bandwidth of a single disk drive. These studies investigate either disk scheduling [RW94, TPBG93] or the placement of data across the surface of a disk drive [CL93, RV93] to enhance the performance of the disk ....

....continuous media data types has been investigated in several earlier studies, including [AH91, RVR92, RV93, CL93, TPBG93, RW94] All studies assume that the bandwidth required to display an object is lower than the bandwidth of a single disk drive. These studies investigate either disk scheduling [RW94, TPBG93] or the placement of data across the surface of a disk drive [CL93, RV93] to enhance the performance of the disk subsystem. They develop admission control policies that enable a system to guarantee a continuous display for each active request. While [TPBG93] assumes a RAID [Pat93] as its target ....

A. L. N. Reddy and J. C. Wyllie. I/O Issues in a Multimedia System. IEEE Computer Magazine, 27(3), March 1994.

....and finally, when Q max = Q min , Q max is the minimum value of q required to store the videos. 8 Related Work A number of storage schemes for continuous retrieval of video and audio data have been proposed in the literature [AOG92, RV91, RV93, GC92, YSB 89, GR93, GS93, BGMJ94, TPBG93, RW94, VGG94, CKY93, LS93, ORS95, ORSM95, CL93, DVV94] However, in every one of the proposed schemes, except for [DVV94] video data is separately retrieved for each request and is not shared among requests as is done by out schemes. In addition, every one of the schemes incurs disk latency overhead ....

....the schemes we have presented in this paper. In [DVV94] the notion of instants that are similar to phases and created dynamically is introduced. However, the issue of retrieving data for the instants from disks is not addressed by the authors. Among the other proposed schemes, AOG92, RV91, GC92, RW94, VGG94, CKY93, CL93, LS93, ORS95] address the problem of satisfying multiple concurrent requests for the retrieval of multimedia objects residing on a disk. These schemes are similar in spirit to the contiguous allocation scheme that we presented in Section 3.1.1. In each of the schemes, ....

[Article contains additional citation context not shown here]

A. L. N. Reddy and J. C. Wyllie. I/O issues in a multimedia system. Computer, 27(3):69--74, March 1994.

....and backward searches. 1 Introduction In recent years, the design of mass storage systems for multimedia applications has become an active research topic. One of the most important applications of multimedia storage systems is on demand playback of video programmes or so called video on demand [1, 2, 3, 4, 5, 6, 7]. In on demand playback applications, the storage system supports concurrent retrieval of continuous video programs requested by a large number of clients. Various video on demand systems support different levels of services [8] In order to meet the realtime bandwidth requirement of ....

A.L. Narasimha Reddy and James C. Wyllie. I/O issues in a multimedia system. IEEE Computer, Vol.27, No.23, pages 69--74, March 1994.

....parameter) different accuracies of advance knowledge, and different service requirements. Storage systems for continuous media, and the associated bandwidth and latency guarantees, make heavy use of scheduling to maximize storage efficiency while providing as much predictability as possible [4, 56]. Network resource scheduling theory may be helpful for advances in storage management, as there are several parallels: In networking terms, advance knowledge of an access pattern is a transfer specification, each storage device and requesting application is a source or destination, and the cache ....

Reddy, A. N., and Wyllie, J. C. I/O issues in a multimedia system. IEEE Computer (March 1994).

....scenarios. Keywords: Multimedia client, resource management, disk scheduling, memory management. 1 Introduction The data for a multimedia presentation (i.e. video and audio) is delivered via a channel from a server to a client. To date, most research has focused on the design of the media server [9, 10, 11, 12, 13, 17, 22, 24, 27, 28, 30, 31], while the media client has received little attention [7, 19, 23, 26] Most research assumes that the client simply has to play back the data as it receives it. In this paper we do focus on the client side, presenting a combined memory disk buffering algorithm that allows the client to ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. Computer, 2:69--74, March 1994.

....Maximizing throughput is a common design objective for a media server. To improve throughput, two approaches have been used: reducing disk latency (i.e. seek overhead and rotational delay) and minimizing the required memory. To reduce disk latency we can either employ efficient disk scheduling [13, 14, 15] or enact intelligent data placement policies [9, 11] Both methods effectively cut down the worst case seek distance for IOs. However, the improvement in throughput that a disk reduction scheme can achieve is limited, since memory, rather than disk, soon becomes the resource bottleneck [6, 7, 8] ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. Computer, 2:69--74, March 1994.

....Techniques for doing so are the subject of this paper. 1.2 Related Work Researchers have proposed various approaches for the storage and retrieval of multimedia data. Anderson et al. AOG92] have proposed file system design techniques for providing hard performance guarantees. Reddy and Wyllie [ReW93, ReW94] have proposed a disk arm scheduling approach for multimedia data, and characterized the disk level tradeoffs in a multimedia server. Rangan et al. RaV92, RVR92] have proposed a model based on constrained block allocation, which is basically noncontiguous disk allocation in which the time taken ....

A. Reddy and J. Wyllie. I/O issues in a multimedia system. IEEE Computer , March 1994.

....The initial latency depends how fast the disk arm can start transferring data for the request. For current disk scheduling algorithms the initial latency can be relatively high. For example, most media server designs use an elevator like disk scheduling policy that we call Sweep in this paper [7, 8, 13, 15, 17, 19]. The Sweep policy amortizes the latency of the disk among the requests it services to reduce the seek overhead. However, if a new request accesses a video segment on the disk that has just been passed by the disk arm, the request must wait until the disk arm finishes the current sweep and returns ....

A. Reddy and J. Wyllie. I/o issues in a multimedia system. Computer, 2:69--74, March 1994.

.... rather than deterministic guarantees) Providing deterministic service at the disk is complicated by the random service time costs involved in disk transfers (because of the random seek and latency overheads) This problem has been addressed effectively by suitable disk scheduling policies [1, 2, 3, 4, 5, 6]. These scheduling 2 policies group a number of requests into rounds or batches and service the requests in a round using a disk seek optimizing policy such as SCAN. Then the service time for the entire round can be bounded to provide guarantees. This strategy works well with CBR streams. An ....

....the deterministic service provided by the system We propose an approach that allows the system to exploit statistical multiplexing while providing deterministic service. Disk service is broken into fixed size time units called rounds or batches. Each round may span 0. 25 1 seconds of time ([1]) In our approach, an application requiring service for a VBR stream supplies the I O system with a trace of its I O demand. This data could be based on frame rate i.e. given on a frame to frame basis or could be more closely tied to the I O system. Specifying the load on a frame basis is more ....

A. L. N. Reddy and J. Wyllie. I/O issues in a multimedia system. IEEE Computer, Mar. 1994.

....requirements of individual streams. Providing deterministic service at the disk is complicated by the random service time costs involved in disk transfers (because of the random seek and latency overheads) This problem has been addressed effectively by suitable disk scheduling policies [1, 2]. These scheduling policies group a number of requests into rounds or batches and service the requests in a round using a disk seek optimizing policy such as SCAN. Then the service time for the entire round can be bounded to provide guarantees. This strategy works well with CBR streams. However, ....

....the deterministic service provided by the system An approach is presented here that allows the system to exploit statistical multiplexing while providing deterministic service. Disk service is broken into fixed size time units called rounds or batches. Each round may span 0. 25 1 seconds of time ([1]) An application requiring service for a VBR stream supplies the I O system with a trace of its I O demand. This data could be based on frame rate i.e. given on a frame to frame basis or could be more closely tied to the I O system. Specifying the load on a frame basis is more flexible and the ....

[Article contains additional citation context not shown here]

A. L. N. Reddy and J. Wyllie. I/O issues in a multimedia system. IEEE Computer, Mar. 1994.

.... rather than deterministic guarantees) Providing deterministic service at the disk is complicated by the random service time costs involved in disk transfers (because of the random seek and latency overheads) This problem has been addressed effectively by suitable disk scheduling policies [13, 14]. These scheduling policies group a number of requests into rounds or batches and service the requests in a round using a disk seek optimizing policy such as SCAN. Then the service time for the entire round can be bounded to provide guarantees. This strategy works well with CBR streams. However, ....

....the deterministic service provided by the system We propose an approach that allows the system to exploit statistical multiplexing while providing deterministic service. Disk service is broken into fixed size time units called rounds or batches. Each round may span 0. 25 1 seconds of time ([13]) In our approach, an application requiring service for a VBR stream supplies the I O system with a trace of its I O demand. This data could be based on frame rate i.e. given on a frame to frame basis or could be more closely tied to the I O system. Specifying the load on a frame basis is more ....

[Article contains additional citation context not shown here]

A. L. N. Reddy and J. Wyllie. I/O issues in a multimedia system. IEEE Computer, Mar. 1994.

....be used to model the behavior of change of sequence requests in an interactive video playback application or the requests in an interactive video game. These requests arrive at irregular intervals of time. Aperiodic requests are regular file requests. Disk scheduling for CBR requests is studied in [1, 2, 3, 4, 5, 6]. Our approach to providing QOS guarantees at the disk is shown in Fig. 1. We employ a two level scheme where bandwidth allocations and resource scheduling are separated. Disk bandwidth is allocated appropriately among the different types of requests. Each class of requests employs an admission ....

A. L. N. Reddy and J. Wyllie. I/O issues in a multimedia system. IEEE Computer, Mar. 1994.

No context found.

A.L. Narasimha Reddy and James C. Wyllie. I/o issues in a multimedia system. IEEE Computer, 27(3):69-- 74, 1994.

No context found.

Reddy, A. and Wyllie, J., 1994. I/O issues in multimedia systems, IEEE Computer vol.27, no.3, pp.6974.

No context found.

A. L. Narasimha Reddy, Jim Wyllie. I/O Issues in a Multimedia System. COMPUTER, 27(3), pp. 69-74, 1994.

No context found.

A. L. N. Reddy, and J. C. Wyllie. I/O Issues in a Multimedia System, IEEE Computer27(3) pp. 69-74, March 1994.

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