• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6B
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• pp.377-386
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• 2005

Recently, to increase throughput per hour on real-time disk scheduling, a lot of algorithms that apply SCAN technique to EDF(Earliest Deadline First) that is representative real-time disk scheduling algorithm are studied. However, existing disk scheduling algorithms have several limitations because they consider continuous I/O requests when create SCAN group. Also, because SCAN technique was fixed direction, the existing algorithms have shortcoming that there are a lot of time damages. This paper proposes a new real-time disk scheduling algorithm based on the insertion technique and the two-way SCAN technique to solve the problems of the exiting real-time disk scheduling algorithms in hard real-time system. The simulation result shows that, when using our techniques, the disk throughput and the number of serviceable I/O requests are enhanced.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.88-95
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• 2004

The previous disk scheduling schemes for best-effort applications do not guarantee the real-time requirement of multimedia objects and the real-time disk scheduling schemes do not satisfy throughput of multimedia server. So, this paper propose a two-step disk scheduling scheme to satisfy the requirement of best-effort as well as soft real-time applications. This scheme is based on the round robin algorithm that imposes different weights on the best-effort task and the real-time one. The experiment results on the Linux kernel have shown that both best-effort tasks and real-time tasks could get fair service.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.2
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• pp.167-178
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• 2000

Software RAID(Redundant Arrays of Inexpensive Disks) is defined as a storage system that provides capabilities of hardware RAID, and guarantees high reliability as well as high performance. In this paper, we propose an enhanced disk scheduling algorithm and a scheme to guarantee reliability of data. We also design and implement software RAID by utilizing these mechanism to develop a storage system for multimedia applications. Because the proposed algorithm improves a defect of traditional GSS algorithm that disk I/O requests arc served in a fixed order, it minimizes buffer consumption and reduces the number of deadline miss through service group exchange. Software RAID also alleviates data copy overhead during disk services by sharing kernel memory. Even though the implemented software RAID uses the parity approach to guarantee reliability of data, it adopts different data allocation scheme. Therefore, we reduce disk accesses in logical XOR operations to compute the new parity data on all write operations. In the performance evaluation experiments, we found that if we apply the proposed schemes to implement the Software RAID, it can be used as a storage system for small-sized video-on-demand servers.

• Journal of the Korea Society of Computer and Information
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• v.16 no.12
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• pp.131-137
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• 2011

Operating Systems is a discipline which handles complex and abstract concepts related to its components and the principles of how an operating system works. However, most of the OS courses have been textbook-oriented theoretical classes. For students who are familiar with various kinds of media, theoretical classes lead to a decline in the understanding of a lecture and difficulty concentrating. They have tried to make use of educational tools to help students understand a lecture and arouse their interests consistently. This paper describes the design and implementation of a disk scheduling simulator which shows the service processes of disk I/O requests visually. The disk scheduling simulator can be used for demonstrations of the disk scheduling algorithms. The results of the academic achievement evaluation and survey showed that a disk scheduling simulator is useful as an educational tool which causes the interests about operating systems and enhances the understanding of a lecture.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.676-678
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• 2002

In this work, we present the novel scheduling algorithm of the multimedia data retrieval for the mobile disk drive. Our algorithm is focused on minimizing the power consumption involved in data retrieval from the local disk drive. The prime commodity in mobile devices is the electricity. Strict restriction on power consumption requirement of the mobile device put unique demand in designing of its hardware and software components. State of the art disk based storage subsystem becomes small enough to be embedded in handhold devices. It delivers abundant storage capacity and portability. However, it is never be trivial to integrate small hard disk or optical disk drive in handhold devices due to its excessive power consumption. Our algorithm ARM in this article generates the optimal schedule of retrieving data blocks from the mobile disk drive while guaranteeing continuous playback of multimedia data.

• The KIPS Transactions:PartA
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• v.12A no.5 s.95
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• pp.355-364
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• 2005

With fast advances in computing power and network technologies, online streaming services of continuous media (CM) have been popularly implemented on the Web. To implement such services, a variety of CM streams need to be processed efficiently, so that the Sweep scheme was proposed. This scheme has several advantages such as hiccup-free playbacks and seek-time optimization. In this scheme, however, the entire CM streams are scheduled with a single scheduling period, called a cycle. Since only one scheduling period is allowed in this scheme, a significant amount of disk time is usually wasted because of its inflexible disk schedules. To solve this, we propose a new dynamic Sweep scheme. For this, we devise an algorithm that is able to expand scheduling periods of serviced CM streams and propose a new admission control mechanism guaranteeing hiccup-free playbacks. To show performance gains, we execute various simulation experiments. From the experimental results, we can see that the proposed scheme outperforms the Sweep scheme in terms of disk utilization and scheduling flexibility.

• The KIPS Transactions:PartA
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• v.11A no.7 s.91
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• pp.547-554
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• 2004

To play back CM (Continuous Media) in online mode, the multimedia system Is required to have a real-time disk scheduling scheme that can efficiently fulfill the strict temporal constraints of serviced CM streams to prevent hiccups. In general, such disk scheduling is performed based on the concept of periodic prefetching since a CM stream has a rather long Playback time. In this paper, we also propose a periodic prefetching scheme that runs by using real-time disk channels, called on-time delivery channels. Since the channels are generated from the bulk-SCAN algorithm and they can be allocated in a very flexible manner based on the EDF (earliest-deadline-first) algorithm, the proposed scheme provides a better Performance in terms of I/O throughput and the average response time, as well as hiccup-free playback of concurrent CM streams. To show that the proposed scheme outperforms other methods, we give some simulation results.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.4
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• pp.242-255
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• 2006

In the recent years, Popularization of mobile devices such as Smart Phones, PDAs and MP3 Players causes rapid increasing necessity of Power management technology because it is most essential factor of mobile devices. On the other hand, despite low price, hard disk has large capacity and high speed. Even it can be made small enough today, too. So it appropriates mobile devices. but it consumes too much power to embed In mobile devices. Due to these motivations, in this paper we had suggested methods of minimizing Power consumption while playing multimedia data in the disk media for real-time and we evaluated what we had suggested. Strict limitation of power consumption of mobile devices has a big impact on designing both hardware and software. One difference between real-time multimedia streaming data and legacy text based data is requirement about continuity of data supply. This fact is why disk drive must persist in active state for the entire playback duration, from power management point of view; it nay be a great burden. A legacy power management function of mobile disk drive affects quality of multimedia playback negatively because of excessive I/O requests when the disk is in standby state. Therefore, in this paper, we analyze power consumption profile of disk drive in detail, and we develop the algorithm which can play multimedia data effectively using less power. This algorithm calculates number of data block to be read and time duration of active/standby state. From this, the algorithm suggested in this paper does optimal scheduling that is ensuring continual playback of data blocks stored in mobile disk drive. And we implement our algorithms in publicly available MPEG player software. This MPEG player software saves up to 60% of power consumption as compared with full-time active stated disk drive, and 38% of power consumption by comparison with disk drive controlled by native power management method.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.2
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• pp.49-56
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• 2007

MEMS-based storage is being developed as a new storage media. Due to its attractive features such as high-bandwidth, low-power consumption, high-density, and low cost, MEMS storage is anticipated to be used for a wide range of applications from storage for small handhold devices to high capacity mass storage servers. However, MEMS storage has vastly different physical characteristics compared to a traditional disk. First, MEMS storage has thousands of heads that can be activated simultaneously. Second, the media of MEMS storage is a square structure which is different from the platter structure of disks. This paper presents a new request scheduling algorithm for MEMS storage that makes use of the aforementioned characteristics. This new algorithm considers the parallelism of MEMS storage as well as the seek time of requests on the two dimensional square structure. We then extend this algorithm to consider the aging factor so that starvation resistance is improved. Simulation studies show that the proposed algorithms improve the performance of MEMS storage by up to 39.2% in terms of the average response time and 62.4% in terms of starvation resistance compared to the widely acknowledged SPTF (Shortest Positioning Time First) algorithm.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.10
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• pp.550-560
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• 2002

External sort on cluster computers requires not only fast internal sorting computation but also careful scheduling of disk input and output and interprocessor communication through networks. This is because the overall time for the execution is determined by reflecting the times for all the jobs involved, and the portion for interprocessor communication and disk I/O operations is significant. In this paper, we improve the sorting performance (sorting throughput) on a cluster of PCs with a low-speed network by developing a new algorithm that enables even distribution of load among processors, and optimizes the disk read and write operations with other computation/communication activities during the sort. Experimental results support the effectiveness of the algorithm. We observe the algorithm reduces the sort time by 45% compared to the previous NOW-sort[1], and provides more scalability in the expansion of the computing nodes of the cluster as well.