System for maintaining a quality of service in a multimedia datastream

Abstract

A real-time write function is provided for a multimedia server system by reserving appropriate disk bandwidth for real-time needs at system configuration time. Blocks of a real-time record are avoided irrespective of the duration of the record which otherwise would occur while awaiting availability of system resources. A preseleted number of disk blocks are pre-allocated so as to keep ahead of the writing real-time application by a designated amount. A system administrative interface is provided to specify before and during the write the duration that the system is to keep ahead of the writing real-time application. Given the duration and the rate at which the application intends to write or record, the number of pre-allocated disk addresses is computed. The addresses are kept in a pre-allocation table maintained on a 'per-open instance' basis. A real-time write application also reserves a determined number of prefetch buffers. A multimedia file system utilizes these buffers to store the application data, attaching deadlines by which these buffers are to be written to the multimedia file system. Every time a prefetch buffer is released, a determination is made that enough pre-allocated disk addresses are ready to be used without delay. The application is thereby assisted in sustaining the desired datastream rate it has specified and been granted by the multimedia file system.