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The size of the Bitcoin blockchain is reaching 350 MB and adding more than 60GB per year. I feel verification node centralization a risk if the cost of storage does not drop.

My question 1: Is using pruned nodes as good as full nodes?

  1. I think a pruned node will have the same UTXOs as a full node (with a full blockchain) and it should be able to verify all incoming transactions and blocks.
  2. It will not be able to provide blocks to a requesting node if it does not have them in its blockchain. But as long as newer nodes have the hash of the previous block this should not be a problem.

My question 2: If there are a significant number of pruned nodes on the network will it impact network security?

Is there something I am missing?

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  • So, 1Tb total in ~10yrs. I strongly question your assumption that verification node centralization is a risk if the cost of storage does not drop. 4TB SSD is $400 today, 14TB HDD was $500 (until recently when the miners apparently started buying high capacity drives for proof-of-store coins). Not out of the reach of many people and absolutely not a factor for institutions. It's possible some hobbyist or enthusiast nodes will drop out, but the growth of bitcoin as a value store will ensure that # of full nodes grow fast as many more people/companies get involved. I run 2, myself, 1TB SSDs. – davidbak May 12 at 1:57
  • If SegWit becomes popular we may see blockchain size rising 100GB per year. Currently, it is 60GB. I run one full node on my laptop. – Vizeet Srivastava May 12 at 6:27
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Your points 1 & 2 are both correct. The good news is the only time those old blocks get requested is by new nodes that are still bootstrapping and downloading the blockchain for the first time. As long as those old blocks are available and accessible somewhere, those new nodes will sync up just fine.

Another fact about pruned nodes is they are required to store at least the most recent 288 blocks. So if your node has only been offline for a day, you can still sync up from a pruned peer.

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