Striping for interactive video: Is it worth it?

We study the design of interactive video servers that store videos on disk arrays. In order to avoid the hot-spot problem in video servers it is conventional wisdom to stripe the videos over the disk array using Fine Grained Striping or Coarse Grained Striping techniques. Striping, however, increases the seek and rotational overhead, thereby reducing the throughput of the disk array. Our results indicate that the decrease in throughput is substantial when interactive delays are constrained to be less than 1 second. We show that both a high degree of interactivity and high throughput are achieved by using a narrow striping width and replicating the videos according to the users' request pattern. Specifically, we find that striping over two disks gives the highest throughput when a tight 1 second constraint on interactive delays is imposed. We also demonstrate that localized placement (i.e., no striping at all) performs nearly as well when a good estimate of the user request pattern is available.