Continuous Display of Video Objects using Heterogeneous Disk Subsystems
Borko Furht, Oge Marques · 2003
Continuous media objects, audio and video clips, are large in size and must be retrieved at a pre-specified rate in order to ensure their hiccup-free display [9, 29]. Even with 100 gigabyte disk drives, a video library consisting of 1000 MPEG-2 titles (with an average display time of 90 minutes) requires thirty such disks for data storage.1 Over time such a storage system will evolve to consist of a heterogeneous collection of disk drives. There are several reasons why a system administrator might be forced to buy new disk drives over time. First, the application might require either a larger storage capacity due to introduction of new titles or a higher bandwidth due to a larger number of users accessing the library. Second, existing disks might fail and need to be replaced.2 The system administrator may not be able to purchase the original disk models due to the technological trends in the area of magnetic disks: Approximately every 12 to 18 months, the cost per megabyte of disk storage drops by 50%, its storage space doubles in size, and its average transfer rate increases by 40% [17, 24]. Older disk models are discontinued because they cannot compete in the market place. For example, a single manufacturer introduced three disk models in the span of six years, a new model every two years; see Table 35.1. The oldest model 1 Assuming an average bandwidth requirement of 4 Mbps for each clip, the system designer might utilize additional disk drives to satisfy the bandwidth requirement of this library, i.e., number of simultaneous users accessing the library. 2 Disks are so cheap and common place that replacing failed disks is cheaper than fixing them.