A Comparison of Data Layout Schemes for Multimedia Servers

A multimedia server has to ensure that multimedia objects are eeciently stored and retrieved from the storage devices of the server. The placement policy of media objects onto the storage devices innuences the retrieval process. In this paper, we examine diierent data layout schemes for disk arrays: round-robin, random and hash-ing. First we introduce universal classes of hash functions which are motivated by PRAM-Simulations (parallel random access machine) on DMMs (Distributed Memory Machines). The diierence between simple hashing schemes and random ones is elaborated by analysis and by simulation. From the practical point of view this diierence is negligible. Then we leave the abstract functions and turn to multimedia servers, where we compare the strategies round-robin, random, and hashing by analysis and by simulation, taking diierent user behavior into account. The layout by hashing is superior to the other methods, because it is simpler managed and needs less memory than random and has suucient quality concerning the load balancing of the disks. The round-robin layout is not well suited compared to the random layout and the layout by hashing because some clients access always a highly loaded disk and others always a disk with low load. The round-robin layout treats some users unfair compared to others.