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Comment by voltagex_ | Hacker News Reader

From a comment on that issue:

>Just for fun, there's about 8000 reachable nodes on the network at the time of writing. Assuming that a large portion of the network is unreachable (NAT, filtering, intermittent, just not listening), it's probably safe to assume there's probably at least 50,000 nodes with the complete blockchain. If we XOR just the chainstate, we cause 50000 * 430 MB of disk writes, 50000 * 430 * 2 MB read and write combined, somewhere in the region of 43TB. If we XOR the entire blockchain on disk we cause 50000 * 21000 * 2 MB of IO, around 1.95PB of RW across the wider Bitcoin network. Incredible.

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Just 8000 bitcoin nodes? So much for the People's Distributed Currency.

Those are probably 'full nodes' to participate in the network as a miner or casual user you don't need to run a full node.

Yeah, but if there are just 8,000 nodes, suddenly it seems like it wouldn't be all that hard to hijack the network.

It's possible I misunderstand, and overestimate the value of full nodes.

You're basically right though, there are regular calls on /r/bitcoin for people to run a full node because the number has gone down recently. I decided set one up on my dedicated host due to one of these.

Interesting - I have been meaning to look into how the blockchain works (I missed the get-rich-quick rush and dismissed it all until heard Andreessen explain the reasons)

Anyway - what does being a full node entail?

Simply run bitcoin-qt or bitcoind all the time and make sure that you have port 8333 open to the outside world (if you have a router, this usually means forwarding 8333).

It takes a few hours to a half day for the node to catch up, depending on your bandwidth and CPU, but after that it requires relatively little processing time. But you do need ~20 GB of free hard drive space for the blockchain.

Non-mining nodes just hold and relay validated blocks, they don't do anything that can be hijacked.

Full nodes host the memory pool for the txid's - So they serve a purpose: Making transactions propagate over the network. And serve blocks to nodes that are not up-to-date (And clients).

8000 nodes listening on IPv4. There's probably hundreds of thousands of non listening ones. Not every node is listening, not every wallet is a node. You can still be trustless even without a copy of the blockchain at hand.

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