Loosely coupled mass storage computer cluster

Abstract

A method and apparatus redundantly store data, in particular video data objects, in a distributed computer system having at least three processor systems, each processor system being connected in point to point two way channel interconnection with each other processor system. The data is stored in a redundant fashion both at the computer system level as well as the processor system level. Accordingly, the failure of a single processor does not adversely affect the integrity of the data. The computer system can also overlay a switching system connected in a ring fashion for providing a fault tolerance to the failure of a single connected processor system at the switch level. Accordingly, there results a fault tolerant data distribution system.

Description

[0001] The invention relates generally to mass storage device interconnections and in particular, to a method and apparatus for increasing delivery bandwidth, providing fault tolerance, and input / output load balancing in a multiprocessor computer cluster. BACKGROUND OF THE INVENTION [0002] Modern reliable computer systems require a large capacity mass storage, and large bandwidth access to that mass storage. While disk sizes have increased substantially, for example a typical personal computer today can be configured with over a gigabyte of storage, the bandwidth available to access the storage has improved, but not significantly. Thus, while large volumes of information can be stored, the rate at which the storage can be accessed has not generally changed in the past few years. In particular, considering the requirements of a digital video system for the delivery of constant bit rate video streams such as MPEG-2 digital video streams, it is important to provide a high bandwidth to ...

AI Technical Summary

Benefits of technology

[0010] The method further features the step of reading data, from the computer system, in the absence of a failure of any of the processor systems, over respective ones of the data channel interconnections, whereby the reading step establishes a load balance across the processor systems. In the presence of a failure of one of the processor systems, the reading of data from the computer system features the steps of reading data from each non-failed processor system storing the data, and reading redundant data from the non-failed processor systems in place of the data stored at the failed processor system. Thereafter, the needed data stored at the failed processor system can be recreated using the redundant data and the data read from the non-failed processor systems. In some embodiments of the invention, during the time when a failure has occurred at any processor system, the method may prevent the writing of any data at any processor system until the failed processor system is brought back on line.

[0011] In another aspect, the invention further features the limiting case wherein there are only two processor systems initially. In accordance with this aspect of the invention, the system continues, in the absence of a failure, to provide increased bandwidth by reading succeeding blocks of data from alternate processors in sequence; and, in this manner, effects a load balancing and provides increased read bandwidth compared to a typical so-called “mirrored” system. In a typical mirrored system, data is read from one processor only, the other processor acting as a backup. Thus, in accordance with the invention, data is read from all of the processors thereby providing an increased read bandwidth and load balancing. As noted hereinafter, therefore, the two processor version of the invention, while not providing all of the advantages of the system with a larger number of processors, does allow easy scalability to a processor system having greater capacity, less overhead, and greater bandwidth.

[0015] The apparatus of the invention further features a system in which the controllers read data from the computer system, in the absence of a failure of any processor system, so as to maintain and establish a load balance across the computer system. In the presence of a failure of one of the processor systems, the controllers read data from each non-failed processor system storing the data (over the appropriate dedicated network connection) and read redundant data from each non-failed processor system in place of the data stored at the failed processor system. The requesting processor system can then recreate the data stored at the failed processor using the read data and the redundant data. In a preferred embodiment, an “external” processor can be employed to recreate the data stored at the failed processor, thereby preserving the delivery bandwidth of the system even in the face of a failed processor.

[0018] In another aspect, the redundant switch has n+1 switched systems each switched system having at least two control inputs, four signal inputs, and two signal outputs. Each switched system is connected at one of its outputs to an associated interrupting signal generator and n interrupting output of the associated signal generator is connected to an input of the connected switched system. The switched systems are interconnected in a ring structure so that each switched system is connected to a first and a second nearest neighbor. Each switched system has switching circuitry responsive to the control input for the switched system for selectively switching its inputs to its outputs. A controller provides the control inputs to the switched systems to enable the switched systems to effectively rotate signal switching functions one position in one or both directions around the ring. Thereby, a failed signal generator can be bypassed and the signals on the n first outputs continue uninterrupted.

Problems solved by technology

Modern reliable computer systems require a large capacity mass storage, and large bandwidth access to that mass storage.

The processor reading the disk drives, however, is still “stuck” with a relatively narrow bandwidth.

Accordingly, the amount of data which can be read is limited by the bus to which the drives are connected.

For example, a SCSI bus which, while providing substantial improvements over buses from years ago, is still relatively slow compared to the needs of video applications.

Also, the use of a local RAID-5 controller can combine the outputs of multiple local SCSI buses, but is subject to the failure of the local processor.

Such a failure eliminates access to all the data.

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