Video Servers: “Shared Storage” for Cost Effective Real-time Access

The architecture used in defining a video server has been traditionally based upon the hierarchical storage model of a computer network. This model was typically specified as independent workstations with local storage connected via a high performance network to a more powerful server configured with a larger bank of remote storage. While supporting a large number of workstations or channels, this approach suffered the drawback of high costs and limited real-time availability to media. The channels are only able to offer realtime access to media on local storage (availability to media on the remote storage being limited by availability of the network), while incurring the cost of the server computer as well as the additional overhead of having material stored in multiple locations. — The shared storage approach to building a video server is a result on a different way of looking at bandwidth. This approach starts by defining the bandwidth of a single drive to be the maximum video channel data rate, and the bandwidth to the storage interface to determine the amount of channels. The shared storage video disk recorder model typically involves a high performance, real time storage interface such as Small Computer System Interface (SCSI) and a lower performance inter-channel synchronization/communication mechanism. The model for this is the multi-channel video disk recorder where each channel acts as an independent device with dedicated storage bandwidth. By virtualizing to storage a well designed system allows the total number of channels to be equal to the storage bandwidth divided by the maximum channel bandwidth. — With the advent of combined of advanced storage platforms such as SSA and Fibre Channel (FC), integrating support for multiple initiators (VDR channels) and tarets (storage devices), the topology for an advanced multi-channel “centralized media / distributed access” video server can be realized. FC with the advantage of its diverse supported topologies, will lead to a radical change in the modeling of future video distribution systems. Fibre channel both increases network bandwidth to 100 MB/sec (200 in the future) and supports both fabric, point-to-point, and arbitrated loop interconnections. The immediate benefit is a resulting five fold increase in storage bandwidth by moving from SCSI (fast/wide) to fiber channel arbitrated loop (FC-AL) and the corresponding increase in channel capacity. A 30 channel VDR in itself is a major breakthrough in product capability, while the increase in supported devices to 127 alleviates the total storage restriction. This combined with a clever implementation of RAID (intrinsically supported under FC-AL) eliminates the need for an external RAID controller. — The evolution of disk drives from being simple devices on an independent “storage-only” bus, to being self sufficient targets on an advanced multi-purpose network marks the start of a new paradigm in the design of distributed computing systems. Understanding and incorporating this new design approach into multi-channel VDR systems will pave the way toward the goal of an integrated digital broadcast environment.

Published

1996-10

Content type

Original Research

DOI

10.5594/M00102

ISBN

978-1-61482-925-6