Playout volumes

A real service needs to accommodate a large configuration, with a large optical jukebox, a fast workstation front-end, plus a fast disc cache or just a workstation with a few Gbytes of disc space.

For a larger configuration with a jukebox we can expect to store more low bandwidth media than high bandwidth media. A jukebox with 144 platters, each with a total capacity of 1.2 Gbytes has a total storage area of 172 Gbytes. The amount of media which can be stored is:

• for a video stream which is presented at 2 Mbps then 500 seconds of video would use 1 Gb. Therefore, in 172 Gb we could store 86,000 seconds worth, which is about 1,440 minutes or 24 hours.
• for a video stream which is presented at 128 Kbps then 8,000 seconds of video would use 1 Gb. Therefore, in 172 Gb we could store 1,376,000 seconds worth, which is about 23,000 minutes or 380 hours or 16 days.
• for a video stream which is presented at 32 Kbps then 32,000 seconds of video would use 1 Gb. Therefore, in 172 Gb we could store 5,504,000 seconds worth, which is about 92,000 minutes or 1530 hours or 64 days.

The most common configuration is expected to be a system in which a workstation with a few Gb of disc space can be used as a server. Such a system could still expect to store many hours of audio and video.

The factors to consider for the storage requirements of a large server are related to (a) the total amount of physical data there is, and (b) the volume of data that needs to be recorded or played in either Kbps or Mbps. For the amount of physical data we need to consider file size, partition size, disc size as well as file structure; for the volume of data we need to consider: disc speed, disc bandwidth, network speed network bandwidth as well as read/write delay seek times, platter load times.

A full investigation of storage for high bandwidth video-on-demand servers can be found in [#!cherve!#] In this section there is just an overview of the issues that need to be considered for the storage requirements of the server.