Fault Tolerance

Brian Randell - Software fault tolerance 1 Beginning in the 1970s, Randell "set up the project that initiated research into the possibility of software fault tolerance, and introduced the "recovery block" concept. Subsequent major developments included the Newcastle Connection, and the prototype distributed Secure System".

Byzantine fault tolerance 1 Byzantine fault tolerance

Byzantine fault tolerance 1 Byzantine fault tolerance is a sub-field of fault tolerance research inspired by the Byzantine Generals' Problem, which is a generalized version of the Two Generals' Problem.

Byzantine fault tolerance 1 The objective of Byzantine fault tolerance is to be able to defend against Byzantine failures, in which components of a system fail in arbitrary ways (i.e., not just by stopping or crashing but by processing requests incorrectly, corrupting their local state, and/or producing incorrect or inconsistent outputs.). Correctly functioning components of a Byzantine fault tolerant system will be able to correctly provide the system's service assuming there are not too many Byzantine faulty components.

Byzantine fault tolerance - Failure modes 1 When a Byzantine failure has occurred, the system may respond in any unpredictable way, unless it is designed to have Byzantine fault tolerance.

Byzantine fault tolerance - Origin 1 Byzantine fault tolerance can be achieved, if the loyal (non-faulty) generals have a unanimous agreement on their strategy. Note that if the source general is correct, all loyal generals must agree upon that value. Otherwise, the choice of strategy agreed upon is irrelevant.

Byzantine fault tolerance - Early solutions 1 A second solution requires unforgeable signatures (in modern computer systems, this may be achieved in practice using public-key cryptography), but maintains Byzantine fault tolerance in the presence of an arbitrary number of traitorous generals.

Byzantine fault tolerance - Practical Byzantine fault tolerance 1 Byzantine fault tolerant replication protocols were long considered too expensive to be practical. Then in 1999, Miguel Castro and Barbara Liskov introduced the "Practical Byzantine Fault Tolerance" (PBFT) algorithm, which provides high-performance Byzantine state machine replication, processing thousands of requests per second with sub-millisecond increases in latency.

Distributed file system for cloud - Fault tolerance 1 For fault tolerance, a chunk is replicated onto multiple chunkservers, by default on three chunckservers. A chunk is available on at least a chunk server.

Application delivery network - Fault tolerance 1 The ADN provides fault tolerance at the server level, within pools or farms. This is accomplished by designating specific servers as a 'backup' that is activated automatically by the ADN in the event that the primary server(s) in the pool fail.[ 9/1219buyers2.html MacVittie, Lori: Content Switches, Network Computing, July, 2001]

Application delivery network - Fault tolerance 1 The ADN also ensures application availability and reliability through its ability to seamlessly failover to a secondary device in the event of a hardware or software failure. This ensures that traffic continues to flow in the event of a failure in one device, thereby providing fault tolerance for the applications. Fault tolerance is implemented in ADNs through either a network or serial based connection.

System Fault Tolerance 1 'System Fault Tolerance' ('SFT') is a fault tolerant system built into NetWare operating systems. There are three levels of fault tolerance:

System Fault Tolerance 1 * SFT I 'Hot Fix' maps out bad disk blocks on the file system level to help ensure data integrity (fault tolerance on disk block level)

System Fault Tolerance 1 * SFT II is a disk mirroring or duplexing system based on RAID 1; mirroring refers to two disk drives holding the same data, duplexing uses two data channels/controllers to connect the disks (fault tolerance on disk and optionally data channel level).

System Fault Tolerance 1 * SFT III is a server duplexing scheme where if a server (computing)|server fails, a constantly synchronized server seamlessly takes its place (fault tolerance on system level).

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