Questions tagged [fault-tolerance]
28 questions
21
votes
4 answers
Why are directed graphs important?
We have been reading about algorithms for MST, strong-connectivity, routing, etc. in directed graphs.
Also recently people have been doing research for dynamic and fault tolerant algorithms for directed graphs.
But I was wondering if there are any…
chyle
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7
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2 answers
Impossibility for Byzantine Generals Problem where $n \leq 3m$
Wiki: https://en.wikipedia.org/wiki/Byzantine_fault_tolerance
In the paper "Reaching Agreement in the Presence of Faults", M. Pease et al. proved that there is no protocol (of some kind) to solve the problem for $n \leq 3m$, where $n$ stands for…
Lwins
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5
votes
1 answer
Why does RAID-5 require an additional disk for parity blocks?
I know that RAID-5 consists of block-level striping across multiple disks, but using an additional parity-check block on each disk .. and that at least two disks are required for striping.
And it's obvious that each parity block is specific to each…
user6039980
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5
votes
1 answer
What is the algorithm for Blockchain's Byzantine Fault Tolerance?
This person was asked: "Why is a blockchain implementation different than a distributed consensus system like Raft?"
In part of their answer they replied:
For one, Raft is not Byzantine fault tolerant, i.e., not designed to account for arbitrary…
hawkeye
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5
votes
2 answers
What if the electricity goes off while a file is being renamed?
Suppose I'm renaming a file and the electricity goes off right in the middle. Naively, it looks like the file could be in some “half-renamed” state. Maybe the name would have half the old name and half the new name. Or maybe the file could disappear…
Anon
- 63
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4
votes
2 answers
Byzantine generals problem with signed messages (Lamport)
I have some trouble understanding Lamport's paper about the Byzantine generals problem when it comes to signed messages. He showed that, with signed messages, the number of generals must be at least $m+2$ to tolerate $m$ malicious units\faults (for…
Matthias Preu
- 141
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4
votes
2 answers
Message receipt verification in a cluster
At my current project I had a network problem come up for which I could not find a solution. In a peer-to-peer network I needed to send an action to all peers, and each peer was to act on it only if it could verify that all other peers would also…
edA-qa mort-ora-y
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4
votes
1 answer
Lamport's Byzantine Generals Algorithm
I've stumbled at the first OralMessage algorithm in Lamport, et al's paper.
I've searched the web and there are dozens of sites, restating in exactly the same terms and examples, which isn't helping me.
Lamport claims the algorithm can handle…
mattrix
- 61
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4
votes
2 answers
Proof in the "Reaching Agreement in the Presence of Faults"
I am reading the "Reaching Agreement in the Presence of Faults", M. Pease et al and trying to understand their proof for the $n \geq 3m+1$ case.
In the induction step $m \gt 0$ it says the following:
... Any other set satisfying these…
sadolit
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3
votes
0 answers
Why/how are the banking systems that robust?
I'm a developer, so I understand (a bit) how computers work, and how softwares work and fail.
In all softwares I've dealt with (as a developer or as a user), I've always seen small or huge bugs:
Even in systems well designed/implemented you…
Evariste
- 153
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3
votes
1 answer
Iterative Byzantine consensus in directed graphs with unbounded malicious nodes
I've found many articles describing iterative procedures to reach Byzantine agreement on a graph (for instance http://www.crhc.illinois.edu/wireless/papers/icdcn14-vaidya.pdf or http://arxiv.org/pdf/1203.1888v1.pdf) but they all assume that a…
Arthur B
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2
votes
1 answer
How does the Weibull distribution work as fault model in wireless sensor networks?
I am a little bit confused with the concept of using the Weibull distribution or other distribution for fault model. As I understand, in simulation this distribution is often used for modelling a fault in components.
On the other hand when designing…
Anahita k
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2
votes
1 answer
Impossibility condition in the Byzantine Generals problem
I am unable to understand why there is a requirement of 3m+1 generals overall given m traitors. As per my understanding, the steps are as follows:
Each general decides a strategy and forwards their strategy to all the other ($3m$) generals.
Each…
Ingrid Morstrad
- 71
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2
votes
1 answer
How P2P search engines prevent corruption of distributed index by malicious peers?
As a hobby, I am writing a simple and primitive distributed web search engine. It occurred to me that it currently has no protection against malicious peers trying to skew the search results.
The principle idea of the project is:
To store the…
Moonwalker
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2
votes
0 answers
Is this simple Asynchronous Byzantine Consensus Protocol correct?
I'm trying to solve a problem that may arise in a system I am concerned with. It will be uncommon in practice, so I am more concerned about simplicity and correctness than performance. I have N nodes that I want to reach agreement on a boolean…
user1055568
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