Document Type

Technical Report


Computer Science and Engineering

Publication Date






Technical Report Number



Cluster based architectures that employ high performance inexpensive Personal Computers (PCs) interconnected by high speed commodity interconnect have been recognized as a cost-effective way of building high performance scalable Multimedia-On-Demand (MOD) storage servers [4, 5, 7, 9]. Typically, the PCs in these architectures run operating systems such as UNIX that have traditionally been optimized for interactive computing. They do not provide fast disk-to-network data paths and guaranteed CPU and storage access. This paper reports enhancements to the 4.4 BSD UNIX system carried out to rectify these limitations in the context of our Project Massively-parallel And Real-time Storage (MARS) [7]. We have proposed and implemented the following enhancements to a 4.4 BSD compliant public domain NetBSD UNIX operating syste: (1) A new kernel buffer management system called Multimedia M-buf (mmbuf) which shortens the data path from a storage device to network interface, (2) priority queueing within the SCSI driver to differentiate between real-time and non-real-time streams, and (3) integration of these new OS services with a CPU scheduling mechanism called Real Time Upcall [22] and a software disk striping driver called Concatenated Disk (ccd). These enhancements collectively provide quality of service guarantee and high throughput to multimedia stream connections. Our experimental results demonstrate throughput improvements and QOS guarantees on the data path from the disk to network in a MOD server.


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