Solutions based on a RAID disk architecture can achieve high aggregate bandwidth, but at a cost which is unattractive for a teaching environment. In this situation there is typically a small number of clips, each of which is a few minutes long. The server's cache is managed through a knowledge of the activities of all current streams, viz. By maintaining a global map of all current activity it is possible to predict the file data next in demand. In particular, we keep data resident which has been used by one stream, but will be needed by others very soon.
Data used by a stream that has no predicted demand is discarded immediately.
This technique gives the most optimal usage of cache space and much reduces the load placed on the disks. The metadata file also contains a header to allow the the clients to determine the format and type of the data, plus parameters such as the number of blocks and frames, the total playback duration, and so on. The server supports NFS allowing the media directory hierarchy to be searched and manipulated by any host able to act as an NFS client. This approach has the advantage of not over-complicating the video server and enabling incorporation with any client system. Thus, the video file server is available to any machine with an ATM network adapter and the appropriate driver software.