Reminder: There have been numerous Bitcoin downtime events that lasted longer than 2 hours, including 5 that lasted over a whole day

People love to mention short outages on faster blockchains, but it's good to keep in mind that Bitcoin routinely has hours of downtime due to its reliance on PoW mining.

There were 5 times when Bitcoin did not produce a block for an entire day.

Bitcoin has 3 different categories of downtime:

1. Blocks taking forever because no one is mining. Keep in mind that Satoshi and a few others were the sole miners for much of the early days. So if they all turned off their mining computers at the same time, that results in downtime.
2. Block taking forever due to random chance. The chance of a block randomly taking longer than 120 minutes to mine is 0.00061%, or once every 3.1 years.
3. Major reorgs in which hours of Bitcoin blocks are reversed. These types of downtime are considered actual "outages".

Longest Bitcoin non-reorg downtimes:

The longest time Bitcoin went without a block was 5 days and 8 hours. There have been other periods of time with 1+ days without a block.

• Block 1 (actually the 2nd block) – Took 5 days, 8 hours to mine. We can let this slide.
• Block 15324 – 1 day, 1 hour (May 22, 2009)
• Block 16564 – 1 day, 1 hour (June 05, 2009)
• Block 15 – 1 day (Jan 9, 2009)
• Block 16592 – 1 day (Jun 6, 2009)
• Block 74638 – 6 hours, 51 min (Aug 15, 2010)
• Block 32647 – 3 hours, 29 min (Jan 2, 2010)
• Block 32629 – 3 hours, 6 min (Jan 2, 2010)
• Most recent: Block 679786 – 122 minutes (Apr 19, 2021)
• There are at least 8 other cases of blocks taking longer than 2 hours prior to 2014.

As of 2021, there had been 190 blocks that took over 106 minutes. This is probably well over 200 blocks by now.

• Chance of a block lasting past 60 minutes: exp(-60/10)*100% => 0.25%, or once every 2.8 days
• Chance of a block lasting past 120 minutes: exp(-120/10)*100 => 0.00061%, or once every 3.1 years

Longest Bitcoin reorg outages (hard forks)

These hours-long outages were caused by bug fixes that required hard forks to fix.

• 51 blocks in Aug 2010 – Caused Bitcoin to mint 184.4 billion Bitcoins, way past its 21 million cap
• 24 blocks on Mar 12, 2013 – Berkeley DB to LevelDB accidentally removed an unknown 10,000-BDB database lock limit and caused a chain split. Required another hard fork to revert.
• Source: https://blog.bitmex.com/bitcoins-consensus-forks/