pull down to refresh

Bitcoin's algorithm is to adjust difficulty to reach the "target' of 10 minutes per block.
But, as you mention, variance can make it so some blocks come quicker, and some occur much slower. But that is not "downtime". Downtime is defined in the Webster dictionary as
Time during which production is stopped especially during setup for an operation or when making repairs
Since there is no centralized method to "halt" miners from adding blocks, there technically never is a stoppage that meets that that definition for downtime. The last incident that is treated as "downtime" (March, 2013) was the result of an erroneous assumption made with software included in what was at the time a new release of the bitcoin client. Technically nothing was "halted", since blocks continued to come, but since the resolution was to have miners "switch back" to the earlier release, the result was a blockchain reorg that affected blocks more than six deep, that was essentially a "disruption" to service, as the expectation that transactions with six or more confirmations could effectively be considered "final" and non-reversible. At least one "confirmed" transaction was double spent (it was for $10K worth of bitcoin), which meets my definition of a "disruption". I personally don't consider variance in the time to solve a block as being a disruption, even a block that took two hours.
I agree. In technical terms, the 2013 "switch back" should be considered a downtime event and block variance should not be considered downtime.
I think I'm more approaching this from layman's terms perspective. Bitcoin is usually explained as "10 minute blocks, give or take", so 2 hours for a block does seem like something isn't working. In the event the network loses a significant portion of the miners (network split like Bitcoin Cash, DDOS attack on pools, etc.) blocks could take even more hours to be found. I think at a certain point, it would be rational to claim the network is not working as designed, if blocks are taking much longer than 10 minutes to be found and the mempool is growing drastically.
reply
if blocks are taking much longer than 10 minutes to be found and the mempool is growing drastically.
That is not bitcoin's design.
Bitcoin's design is to, over a long period of time, have the average ~10 minutes per block. A block taking an hour can be a daily occurrence. You can't say a system has failed to perform when it performs as it was designed. You can say the design is a failure, but that's a different argument.
reply