Placement of multimedia blocks on zoned disks

Abstract

We examine the impact on optimal data placement schemes for random retrieval due to a new trend in disk technology, namely zoned magnetic disks, which record data with a constant linear density and have a constant angular velocity. This modifies the optimal data placement that minimizes response time, since now the data transfer time varies with block placement whereas the transfer time and cylinder capacity was constant for traditional magnetic disks. We focus on the optimal placement of video objects stored in multimedia servers that consist of fixed-size blocks of constant-bit-rate encoded data or varying-size blocks of variable-bit-rate encoded data. The differences in popularity and access rates among these objects allow minimization of seek times by varying the data placement. We describe an optimal placement of fixed-size blocks on zoned disks that minimizes response time. Video objects are accessed by streams that playout the blocks at a given rate, requiring disk access by a deadline in order to avoid glitches in playout. For the placement of varying-size blocks on zoned disks, we study a scheme that minimizes the probability that a block access misses its deadline. This is done by adjusting the value representing the popularity of blocks to take into account both block size and the relative importance of seek time and transfer time using a weighting factor. We quantify the improvements in disk throughput for a given block-deadline miss probability. ©2004 Copyright SPIE - The International Society for Optical Engineering.