Performance of a storage system for supporting different video types and qualities

Future video-on-demand (VoD) servers will need to support many existing and emerging video data types. These data types include 15-fps (frames per second) animation, 30-fps National Television Systems Committee (NTSC) quality video, and 60-fps high definition television (HDTV) video. The different display speeds and frame sizes of these various video types impose a major constraint on the design of VoD storage systems. This paper presents the results of an experimental study, conducted on a Silicon Graphics Inc. (SGI) Onyx computer system, that investigated the impact of these video types on the design of a VoD storage system. The key issues involved in supporting these different video types in a VoD environment are as follows: (1) the video allocation method and (2) the proper block size (a "block" is a basic unit of several contiguous video frames that will be accessed from several disks each time a request is made) to use for data striping and retrieval. Two allocation schemes, logical volume striping and application level striping, along with varying frame and block sizes for each of the three different video data types are examined. The focus of our study is to determine the maximum number of concurrent accesses that can be supported with a guaranteed quality-of-service (QoS). The degree of scalability (i.e., striping data over more disk arrays) of the experimental VoD system used is also studied. Based on our experimental results, application level striping demands smaller block sizes for all three video types, and more concurrent accesses can be distributed over the storage devices. The experimental results demonstrate that application level striping has excellent scalability for animation and NTSC videos.