Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1997-10-02
2001-09-18
Lee, Thomas (Department: 2182)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S011000, C709S239000
Reexamination Certificate
active
06292905
ABSTRACT:
APPENDICES
Appendix A, which forms a part of this disclosure, is a list of commonly owned copending U.S. patent applications. Each one of the applications listed in Appendix A is hereby incorporated herein in its entirety by reference thereto.
Appendix B, which forms part of this disclosure, is a copy of the U. S. provisional patent application filed May 13, 1997, entitled “Clustering Of Computer Systems Using Uniform Object Naming And Distributed Software For Locating Objects,” and assigned application Ser. No. 60/046,327.
COPYRIGHT AUTHORIZATION
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention pertains to computer networks. More particularly, this invention relates to improving the ability of a network to route around faulty components.
2. Description of Related Art
As computer systems and networks become more complex, various systems for promoting fault tolerance have been devised. To prevent network down-time due to power failure, uninterrupted power supplies (UPS) have been developed. A UPS is basically a rechargeable battery to which a workstation or server is connected. In the event of a power failure the workstation or server is maintained in operation by the rechargeable battery until such time as the power resumes.
To prevent network down-time due to failure of a storage device, data mirroring was developed. Data mirroring provides for the storage of data on separate physical devices operating in parallel with respect to a file server. Duplicate data is stored on separate drives. Thus, when a single drive fails the data on the mirrored drive may still be accessed.
To prevent network down-time due to a print/file server, server mirroring has been developed. Server mirroring as it is currently implemented requires a primary server and storage device, a backup server and storage device, and a unified operating system linking the two. An example of a mirrored server product is the Software Fault Tolerance level 3 (SFT III) product by Novell Inc., 1555 North Technology Way, Orem, Utah, as an add-on to its NetWare® 4.x product. SFT III maintains servers in an identical state of data update. It separates hardware-related operating system (OS) functions on the mirrored servers so that a fault on one hardware platform does not affect the other. The server OS is designed to work in tandem with two servers. One server is designated as a primary server, and the other is a secondary server. The primary server is the main point of update; the secondary server is in a constant state of readiness to take over. Both servers receive all updates through a special link called a mirrored server link (MSL), which is dedicated to this purpose. The servers also communicate over the local area network (LAN) that they share in common, so that one knows if the other has failed even if the MSL has failed. When a failure occurs, the second server automatically takes over without interrupting communications in any user-detectable way. Each server monitors other server's NetWare Core Protocol (NCP) acknowledgments over the LAN to see that all the requests are serviced and that OSs are constantly maintained in a mirrored state.
When the primary server fails, the secondary server detects the failure and immediately takes over as the primary server. The failure is detected in one or both of two ways: the MSL link generates an error condition when no activity is noticed, or the servers communicate over the LAN, each one monitoring the other's NCP acknowledgment. The primary server is simply the first server of the pair that is brought up. It then becomes the server used at all times and it processes all requests. When the primary server fails, the secondary server is immediately substituted as the primary server with identical configurations. The switch-over is handled entirely at the server end, and work continues without any perceivable interruption.
Power supply backup, data mirroring, and server mirroring all increase security against down time caused by a failed hardware component, but they all do so at considerable cost. Each of these schemes requires the additional expense and complexity of standby hardware, that is not used unless there is a failure in the network. Mirroring, while providing redundancy to allow recovery from failure, does not allow the redundant to be used to improve cost/performance of the network.
What is needed is a fault tolerant system for computer networks that can provide all the functionality of UPS, disk mirroring, or server mirroring without the added cost and complexity of standby/additional hardware. What is needed is a fault tolerant system for computer networks which smoothly interfaces with existing network systems.
SUMMARY OF THE INVENTION
In an embodiment of the invention, the method comprises the acts of:
providing a network resource database, the database includes individual records corresponding to clustered network resources, and for the clustered resources, the database includes a first record corresponding to the network resource, and the first record identifies the primary server for the network resource as the first server;
selecting, on the basis of the first record, the first server to provide service to the client workstation with respect to that clustered network resource;
recognizing the backup server for that clustered network resource as the second server;
detecting a failure of the first server; and
routing communications between the client workstation and the network resource via the second server, responsive to the recognizing and detecting acts.
In another embodiment of the invention, the method comprises the additional acts of:
identifying in the first record, the primary server for the network resource as the first server;
discovering a recovery of the first server; and
re-routing communications between the client workstation and the network resource via the first server, responsive to the identifying and discovering acts.
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Chrabaszcz Michael
Findlay Bruce
Pellicer Thomas J.
Wallach Walter A.
Knobbe Martens Olson & Bear LLP
Lee Thomas
Micro)n Technology, Inc.
Nguyen Nguyen
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