Although modification operations on multimedia data such as insertion and/or deletion of video clips are rare, they may cause significant degradation of disk I/O performance in disk-array-based video servers. This is because many existing disk-array-based video servers consider only video playback at normal speed and retrieval-oriented VCR-like operations such as fast-forward and rewind without considering relocation of video data. Most conventional video servers provide optimal performance using static placement of video data on multiple disks. In this paper, we propose a method called 'SRM (Segment Relocation Method)' which provides uniform loadbalance of disks regardless of the dynamic modification of stored video objects. For modification operations, the segments belonging to the corresponding 'round' of disk placement are relocated so that the system guarantees uniform load-balance of multiple disks in all rounds. To justify the significance of the relocation scheme, we evaluate and compare the cost of retrieval in terms of the required buffer size and the number of admitted users.
Multimedia data, especially continuous media including video and audio objects, represent a rich and natural stimulus for humans, but require large amount of storage capacity and real-time processing. In this paper, we describe how to organize video data efficiently on multiple disks in order to support arbitrary-rate playback requested by different users independently. Our approach is to segment and decluster video objects and to place the segments in multiple disks using a restricted round-robin scheme, called prime round-robin (PRR). Its placement scheme provides uniform load balance of disks for arbitrary retrieval rate as well as normal playback, since it eliminates hot spots. Moreover, it does not require any additional disk bandwidth to support VCR-like operations such as fast-forward and rewind. We have studied the various effects of placement and retrieval schemes in a storage server by simulation. The results show that PRR offers even disk accesses, and the failure in reading segment by deadline occurs only at the beginning of new operations. In addition, the number of users admitted is not decreased, regardless of arbitrary-rate playback requests.
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