Not sure what you mean with "safety critical". I made no such assumption. Also since the topic is about a (write-only) log it probably doesn't need such low latency. What it more likely needed is final states so once a entry is made and accepted it must be final and ofc correct. DLTs can do this distributed and self-fixing i.e. a node that tries to add fault data is overruled and can never get a confirmation for a final state that later would not be valid.

Getting the whole decentral system to "agree" will never be fast unless we have quantum tech. There is simply no way servers around the glob could communicate in microseconds even if all communication would be the speed of light and processing would be instant. It would still take time. In reality such system need seconds which is often totally fine. As long as everyone only relies on the data that has been declared final.

You said If a system is critical

I thought you were making a more general statement about all critical systems, that's all. And since many critical systems have a safety factor in play, I wanted to distinguish them as not always being a good target for a Blockchain solution to the problems of consensus.

Blockchain is a very interesting solution to the problem of obtaining consensus in the face of imperfect inputs, there are other options so, like anything else, you choose the right tool for the job. My own view is that-- given other established protocols, blockchain is going to be overkill for dealing with some types of fault tolerance. It is a very good fit for applications where you want to minimize relying on the trust of humans. (And other areas too, but right now I'm just speaking of the narrow context of consensus amid inconsistent inputs)

Critical that the system operates/keeps operating/does not reach an invalid state. It could be for safety but in general its more to avoid financial damage. Downtime of any kind usually result in huge financial loses and people working extra shifts. This was my main point.

>...blockchain is going to be overkill for dealing with some types of fault tolerance

But it this case likely it isn't. The current systen already works with a chain of blocks its just lacks the distributed checking and all that stuff. But "blckchains" aren't some secret sauce in this case it just an way to implement a distributed write-only database with filed proven tech. It can be as lightweight as it any other solution. The consensus part is completely irrelevant anyway because all nodes are operated by one entity. But due to the use case (money/value) of modern DLT ("blockchains") they are incredible reliable by design. The oldest DLTs that uses FBA (instead of PoW/PoS) are running since 9+ years without any error or downtime. Recreating a similar reliable system would be month and month of work followed by month of testing.

Yep, pretty much agreed. Whatever anyone may think if crypto currencies blockchains are essentially a different technology where coins are just 1 application. I'm kind of "meh" on crypto currencies (not anti, just think they need a while more to mature) but trustless consensus is a significant innovation in its own right.