<p>It is technically possible that all copies of the blockchain are lost...but extremely unlikely.  Also, I see no reason why such a massive data loss would be restricted to a single historical block, rather than the whole blockchain.</p>

<p>For a cool visualization of the number of full nodes on the network, look here:</p>

<p><a href="https://bitnodes.21.co/nodes/network-map/" rel="nofollow">https://bitnodes.21.co/nodes/network-map/</a></p>

<p>Keep in mind that there are probably a lot more copies of the entire blockchain than there are full nodes.  For example, I run 1 full node from my house, but also have 3 full copies of the blockchain backed up (so I don't have to download again).  It would take a cataclysmic event to destroy all the world's backups.</p>

<p>Also, having worked IT for a bank, I can assure you that your bank account doesn't have nearly this many redundant backups.</p>

CC BY-SA 3.0
2016-07-04T16:40:05.290Z
Thank you Jestin for your answer. How do I have to read the nodes of the network map ? The positions are random ? geograhical ?
John Smith
CC BY-SA 3.0
2016-07-05T01:13:28.573Z
I'm not sure on the specifics, but I'm sure there's an explanation on the site if you look around.  I just thought it was a cool visualization ;)
Jestin
CC BY-SA 3.0
2016-07-04T13:52:16.970Z
2016-07-04T13:52:16.970Z
Jestin
<p>The blockchain is called a block<strong>chain</strong> because each block references a previous block that it builds on top of. The way bitcoind is structured, it would take a malicious bug to destroy a particular block without affecting others (in which case all blocks that come after said block would be invalid). So unless there's some super-virus that affects every single copy of the blockchain to destroy a particular block, this is near impossible to lose "1 block".</p>

<p>There are thousands of full nodes that store a complete copy of the blockchain, and services like blockchain.info and blockcypher.com have many redundant copies and backups of the blockchain to ensure it's not lost.</p>

<p>There are instances when blocks are invalidated or orphaned, because another block was found with the appropriate proof-of-work and then extended instead of the orphaned block. This is probably the only instance in which a block could be considered "lost".</p>

CC BY-SA 3.0
2016-07-04T14:44:47.007Z
2016-07-04T14:44:47.007Z
Jimmy Song
<p>Not really. There are thousands of copies of the complete blockchain, and if one node lost a block it could easily regain it from a peer.</p>

<p>As blocks cannot be validated without the complete chain of their ancestors up to the genesis block, losing one block would be equivalent to losing confidence in all blocks that succeeded it. This <em>orphaned</em> chain would be considered invalid without a link to its ancestors.</p>

CC BY-SA 3.0
2016-07-04T15:32:32.653Z
2016-07-04T15:32:32.653Z
Murch
<p>Since the blockchain is stored in a distributed database, is it possible that one block can be lost? Then it would be impossible to link future blocks to previous blocks.</p>

<p>How many copies of the blockchain are there?</p>

CC BY-SA 3.0
2016-07-04T15:10:43.750Z
Hi XR SC, Welcome to Bitcoin.Stackexchange.com. Could you please stop putting the [tag:zero-knowledge] tag on your questions? It refers to a specific concept in cryptography that was not related to any of your questions so far.
Murch
CC BY-SA 3.0
2016-07-04T16:38:56.457Z
Cool, thank you for your comment. In fact, I thought that zero knowledge means: "I have no knowledge of bitcoin" :)
John Smith
CC BY-SA 3.0
2016-07-04T22:50:54.973Z
Heh, yes, I thought so. :) You might have realized that this site is a bit different than regular forums: Have you seen our [tour]? You've asked a few questions already. Perhaps some have already gathered answers that you found convincing, and you might want to consider accepting one of the answers. :) Besides that, carry on!
Murch
<blockchain><full-node>
Can an intermediary block be lost?
John Smith
# Can an intermediary block be lost?

(Asked by: username_0 on 2016-07-04)

Since the blockchain is stored in a distributed database, is it possible that one block can be lost? Then it would be impossible to link future blocks to previous blocks.

How many copies of the blockchain are there?

**Tags:** blockchain, full-node

> **Comments:**
> **username_1**: Hi XR SC, Welcome to Bitcoin.Stackexchange.com. Could you please stop putting the [tag:zero-knowledge] tag on your questions? It refers to a specific concept in cryptography that was not related to any of your questions so far.  
> **username_0**: Cool, thank you for your comment. In fact, I thought that zero knowledge means: "I have no knowledge of bitcoin" :)  
> **username_1**: Heh, yes, I thought so. :) You might have realized that this site is a bit different than regular forums: Have you seen our [tour]? You've asked a few questions already. Perhaps some have already gathered answers that you found convincing, and you might want to consider accepting one of the answers. :) Besides that, carry on!  

---

## 3 answers

### Answer by username_2 on 2016-07-04. Score: 2 | Accepted answer

It is technically possible that all copies of the blockchain are lost...but extremely unlikely. Also, I see no reason why such a massive data loss would be restricted to a single historical block, rather than the whole blockchain.

For a cool visualization of the number of full nodes on the network, look here:

<https://bitnodes.21.co/nodes/network-map/>

Keep in mind that there are probably a lot more copies of the entire blockchain than there are full nodes. For example, I run 1 full node from my house, but also have 3 full copies of the blockchain backed up (so I don't have to download again). It would take a cataclysmic event to destroy all the world's backups.

Also, having worked IT for a bank, I can assure you that your bank account doesn't have nearly this many redundant backups.

> **Comments:**
> **username_0**: Thank you username_2 for your answer. How do I have to read the nodes of the network map ? The positions are random ? geograhical ?  
> **username_2**: I'm not sure on the specifics, but I'm sure there's an explanation on the site if you look around.  I just thought it was a cool visualization ;)  

---

### Answer by username_3 on 2016-07-04. Score: 2

The blockchain is called a block**chain** because each block references a previous block that it builds on top of. The way bitcoind is structured, it would take a malicious bug to destroy a particular block without affecting others (in which case all blocks that come after said block would be invalid). So unless there's some super-virus that affects every single copy of the blockchain to destroy a particular block, this is near impossible to lose "1 block".

There are thousands of full nodes that store a complete copy of the blockchain, and services like blockchain.info and blockcypher.com have many redundant copies and backups of the blockchain to ensure it's not lost.

There are instances when blocks are invalidated or orphaned, because another block was found with the appropriate proof-of-work and then extended instead of the orphaned block. This is probably the only instance in which a block could be considered "lost".


---

### Answer by username_1 on 2016-07-04. Score: 2

Not really. There are thousands of copies of the complete blockchain, and if one node lost a block it could easily regain it from a peer.

As blocks cannot be validated without the complete chain of their ancestors up to the genesis block, losing one block would be equivalent to losing confidence in all blocks that succeeded it. This *orphaned* chain would be considered invalid without a link to its ancestors.


---

