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Subject: Re: [bitcoin-dev] Small Nodes: A Better Alternative to Pruned Nodes
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??? what do you mean? (https://www.soyoustart.com/fr/serveurs-essential/)
Le 20/04/2017 à 17:50, Erik Aronesty via bitcoin-dev a écrit :
> Try to find 1TB dedicated server hosting ...
>
> If you want to set up an ecommerce site somewhere besides your living
> room, storage costs are still a concern.
>
> On Mon, Apr 17, 2017 at 3:11 AM, Danny Thorpe via bitcoin-dev
> <bitcoin-dev@lists.linuxfoundation.org
> <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>
> 1TB HDD is now available for under $40 USD. How is the 100GB
> storage requirement preventing anyone from setting up full nodes?
>
> On Apr 16, 2017 11:55 PM, "David Vorick via bitcoin-dev"
> <bitcoin-dev@lists.linuxfoundation.org
> <mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>
> *Rationale:*
>
> A node that stores the full blockchain (I will use the term
> archival node) requires over 100GB of disk space, which I
> believe is one of the most significant barriers to more people
> running full nodes. And I believe the ecosystem would benefit
> substantially if more users were running full nodes.
>
> The best alternative today to storing the full blockchain is
> to run a pruned node, which keeps only the UTXO set and throws
> away already verified blocks. The operator of the pruned node
> is able to enjoy the full security benefits of a full node,
> but is essentially leeching the network, as they performed a
> large download likely without contributing anything back.
>
> This puts more pressure on the archival nodes, as the archival
> nodes need to pick up the slack and help new nodes bootstrap
> to the network. As the pressure on archival nodes grows, fewer
> people will be able to actually run archival nodes, and the
> situation will degrade. The situation would likely become
> problematic quickly if bitcoin-core were to ship with the
> defaults set to a pruned node.
>
> Even further, the people most likely to care about saving
> 100GB of disk space are also the people least likely to care
> about some extra bandwidth usage. For datacenter nodes, and
> for nodes doing lots of bandwidth, the bandwidth is usually
> the biggest cost of running the node. For home users however,
> as long as they stay under their bandwidth cap, the bandwidth
> is actually free. Ideally, new nodes would be able to
> bootstrap from nodes that do not have to pay for their
> bandwidth, instead of needing to rely on a decreasing
> percentage of heavy-duty archival nodes.
>
> I have (perhaps incorrectly) identified disk space consumption
> as the most significant factor in your average user choosing
> to run a pruned node or a lite client instead of a full node.
> The average user is not typically too worried about bandwidth,
> and is also not typically too worried about initial blockchain
> download time. But the 100GB hit to your disk space can be a
> huge psychological factor, especially if your hard drive only
> has 500GB available in the first place, and 250+ GB is already
> consumed by other files you have.
>
> I believe that improving the disk usage situation would
> greatly benefit decentralization, especially if it could be
> done without putting pressure on archival nodes.
>
> *Small Nodes Proposal:*
>
> I propose an alternative to the pruned node that does not put
> undue pressure on archival nodes, and would be acceptable and
> non-risky to ship as a default in bitcoin-core. For lack of a
> better name, I'll call this new type of node a 'small node'.
> The intention is that bitcoin-core would eventually ship
> 'small nodes' by default, such that the expected amount of
> disk consumption drops from today's 100+ GB to less than 30 GB.
>
> My alternative proposal has the following properties:
>
> + Full nodes only need to store ~20% of the blockchain
> + With very high probability, a new node will be able to
> recover the entire blockchain by connecting to 6 random small
> node peers.
> + An attacker that can eliminate a chosen+ 95% of the full
> nodes running today will be unable to prevent new nodes from
> downloading the full blockchain, even if the attacker is also
> able to eliminate all archival nodes. (assuming all nodes
> today were small nodes instead of archival nodes)
>
> Method:
>
> A small node will pick an index [5, 256). This index is that
> node's permanent index. When storing a block, instead of
> storing the full block, the node will use Reed-Solomon coding
> to erasure code the block using a 5-of-256 scheme. The result
> will be 256 pieces that are 20% of the size of the block each.
> The node picks the piece that corresponds to its index, and
> stores that instead. (Indexes 0-4 are reserved for archival
> nodes - explained later)
>
> The node is now storing a fragment of every block. Alone, this
> fragment cannot be used to recover any piece of the
> blockchain. However, when paired with any 5 unique fragments
> (fragments of the same index will not be unique), the full
> block can be recovered.
>
> Nodes can optionally store more than 1 fragment each. At 5
> fragments, the node becomes a full archival node, and the
> chosen indexes should be 0-4. This is advantageous for the
> archival node as the encoded data for the first 5 indexes will
> actually be identical to the block itself - there is no
> computational overhead for selecting the first indexes. There
> is also no need to choose random indexes, because the full
> block can be recovered no matter which indexes are chosen.
>
> When connecting to new peers, the indexes of each peer needs
> to be known. Once peers totaling 5 unique indexes are
> discovered, blockchain download can begin. Connecting to just
> 5 small node peers provides a >95% chance of getting 5
> uniques, with exponentially improving odds of success as you
> connect to more peers. Connecting to a single archive node
> guarantees that any gaps can be filled.
>
> A good encoder should be able to turn a block into a 5-of-256
> piece set in under 10 milliseconds using a single core on a
> standard consumer desktop. This should not slow down initial
> blockchain download substantially, though the overhead is more
> than a rounding error.
>
> *DoS Prevention:*
>
> A malicious node may provide garbage data instead of the
> actual piece. Given just the garbage data and 4 other correct
> pieces, it is impossible (best I know anyway) to tell which
> piece is the garbage piece.
>
> One option in this case would be to seek out an archival node
> that could verify the correctness of the pieces, and identify
> the malicious node.
>
> Another option would be to have the small nodes store a
> cryptographic checksum of each piece. Obtaining the
> cryptographic checksum for all 256 pieces would incur a
> nontrivial amount of hashing (post segwit, as much as 100MB of
> extra hashing per block), and would require an additional ~4kb
> of storage per block. The hashing overhead here may be
> prohibitive.
>
> Another solution would be to find additional pieces and
> brute-force combinations of 5 until a working combination was
> discovered. Though this sounds nasty, it should take less than
> five seconds of computation to find the working combination
> given 5 correct pieces and 2 incorrect pieces. This
> computation only needs to be performed once to identify the
> malicious peers.
>
> I also believe that alternative erasure coding schemes exist
> which actually are able to identify the bad pieces given
> sufficient good pieces, however I don't know if they have the
> same computational performance as the best Reed-Solomon coding
> implementations.
>
> *Deployment:*
>
> Small nodes are completely useless unless the critical mass of
> 5 pieces can be obtained. The first version that supports
> small node block downloads should default everyone to an
> archival node (meaning indexes 0-4 are used)
>
> Once there are enough small-node-enabled archive nodes, the
> default can be switched so that nodes only have a single index
> by default. In the first few days, when there are only a few
> small nodes, the previously-deployed archival nodes can help
> fill in the gaps, and the small nodes can be useful for
> blockchain download right away.
>
> ----------------------------------
>
> This represents a non-trivial amount of code, but I believe
> that the result would be a non-trivial increase in the
> percentage of users running full nodes, and a healthier
> overall network.
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> <mailto:bitcoin-dev@lists.linuxfoundation.org>
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> <https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> <mailto:bitcoin-dev@lists.linuxfoundation.org>
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> <https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>
>
>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
--
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<p>??? what do you mean?
(<a class="moz-txt-link-freetext" href="https://www.soyoustart.com/fr/serveurs-essential/">https://www.soyoustart.com/fr/serveurs-essential/</a>)<br>
</p>
<br>
<div class="moz-cite-prefix">Le 20/04/2017 à 17:50, Erik Aronesty
via bitcoin-dev a écrit :<br>
</div>
<blockquote
cite="mid:CAJowKg++8GD3gE15pdwe0Bj-L0A6MAzG0_uTSLASaRT9yVb1aQ@mail.gmail.com"
type="cite">
<div dir="ltr">Try to find 1TB dedicated server hosting ... <br>
<br>
If you want to set up an ecommerce site somewhere besides your
living room, storage costs are still a concern.<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Apr 17, 2017 at 3:11 AM, Danny
Thorpe via bitcoin-dev <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:bitcoin-dev@lists.linuxfoundation.org"
target="_blank">bitcoin-dev@lists.linuxfoundation.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="auto">1TB HDD is now available for under <span
class="m_2752087275107902543money">$40</span> USD. How
is the 100GB storage requirement preventing anyone from
setting up full nodes?</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">
<div>
<div class="h5">On Apr 16, 2017 11:55 PM, "David
Vorick via bitcoin-dev" <<a
moz-do-not-send="true"
href="mailto:bitcoin-dev@lists.linuxfoundation.org"
target="_blank">bitcoin-dev@lists.<wbr>linuxfoundation.org</a>>
wrote:<br type="attribution">
</div>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div class="h5">
<div dir="ltr">
<div>
<div><b>Rationale:</b><br>
</div>
<div><br>
A node that stores the full blockchain (I
will use the term archival node) requires
over 100GB of disk space, which I believe is
one of the most significant barriers to more
people running full nodes. And I believe the
ecosystem would benefit substantially if
more users were running full nodes.<br>
<br>
</div>
The best alternative today to storing the full
blockchain is to run a pruned node, which
keeps only the UTXO set and throws away
already verified blocks. The operator of the
pruned node is able to enjoy the full security
benefits of a full node, but is essentially
leeching the network, as they performed a
large download likely without contributing
anything back.<br>
<br>
</div>
<div>This puts more pressure on the archival
nodes, as the archival nodes need to pick up
the slack and help new nodes bootstrap to the
network. As the pressure on archival nodes
grows, fewer people will be able to actually
run archival nodes, and the situation will
degrade. The situation would likely become
problematic quickly if bitcoin-core were to
ship with the defaults set to a pruned node.<br>
<br>
</div>
<div>Even further, the people most likely to
care about saving 100GB of disk space are also
the people least likely to care about some
extra bandwidth usage. For datacenter nodes,
and for nodes doing lots of bandwidth, the
bandwidth is usually the biggest cost of
running the node. For home users however, as
long as they stay under their bandwidth cap,
the bandwidth is actually free. Ideally, new
nodes would be able to bootstrap from nodes
that do not have to pay for their bandwidth,
instead of needing to rely on a decreasing
percentage of heavy-duty archival nodes.<br>
<br>
</div>
<div>I have (perhaps incorrectly) identified
disk space consumption as the most significant
factor in your average user choosing to run a
pruned node or a lite client instead of a full
node. The average user is not typically too
worried about bandwidth, and is also not
typically too worried about initial blockchain
download time. But the 100GB hit to your disk
space can be a huge psychological factor,
especially if your hard drive only has 500GB
available in the first place, and 250+ GB is
already consumed by other files you have.<br>
<br>
</div>
<div>I believe that improving the disk usage
situation would greatly benefit
decentralization, especially if it could be
done without putting pressure on archival
nodes.<br>
</div>
<div><br>
</div>
<div><b>Small Nodes Proposal:</b><br>
<br>
</div>
<div>I propose an alternative to the pruned node
that does not put undue pressure on archival
nodes, and would be acceptable and non-risky
to ship as a default in bitcoin-core. For lack
of a better name, I'll call this new type of
node a 'small node'. The intention is that
bitcoin-core would eventually ship 'small
nodes' by default, such that the expected
amount of disk consumption drops from today's
100+ GB to less than 30 GB.<br>
<br>
</div>
<div>My alternative proposal has the following
properties:<br>
<br>
</div>
<div>+ Full nodes only need to store ~20% of the
blockchain<br>
</div>
<div>+ With very high probability, a new node
will be able to recover the entire blockchain
by connecting to 6 random small node peers.<br>
</div>
<div>+ An attacker that can eliminate a chosen+
95% of the full nodes running today will be
unable to prevent new nodes from downloading
the full blockchain, even if the attacker is
also able to eliminate all archival nodes.
(assuming all nodes today were small nodes
instead of archival nodes)<br>
<br>
</div>
<div>Method:<br>
<br>
</div>
<div>A small node will pick an index [5, 256).
This index is that node's permanent index.
When storing a block, instead of storing the
full block, the node will use Reed-Solomon
coding to erasure code the block using a
5-of-256 scheme. The result will be 256 pieces
that are 20% of the size of the block each.
The node picks the piece that corresponds to
its index, and stores that instead. (Indexes
0-4 are reserved for archival nodes -
explained later)<br>
<br>
</div>
<div>The node is now storing a fragment of every
block. Alone, this fragment cannot be used to
recover any piece of the blockchain. However,
when paired with any 5 unique fragments
(fragments of the same index will not be
unique), the full block can be recovered.<br>
<br>
</div>
<div>Nodes can optionally store more than 1
fragment each. At 5 fragments, the node
becomes a full archival node, and the chosen
indexes should be 0-4. This is advantageous
for the archival node as the encoded data for
the first 5 indexes will actually be identical
to the block itself - there is no
computational overhead for selecting the first
indexes. There is also no need to choose
random indexes, because the full block can be
recovered no matter which indexes are chosen.<br>
<br>
</div>
<div>When connecting to new peers, the indexes
of each peer needs to be known. Once peers
totaling 5 unique indexes are discovered,
blockchain download can begin. Connecting to
just 5 small node peers provides a >95%
chance of getting 5 uniques, with
exponentially improving odds of success as you
connect to more peers. Connecting to a single
archive node guarantees that any gaps can be
filled.<br>
<br>
</div>
<div>A good encoder should be able to turn a
block into a 5-of-256 piece set in under 10
milliseconds using a single core on a standard
consumer desktop. This should not slow down
initial blockchain download substantially,
though the overhead is more than a rounding
error.<br>
</div>
<div><br>
</div>
<div><b>DoS Prevention:</b><br>
<br>
</div>
<div>A malicious node may provide garbage data
instead of the actual piece. Given just the
garbage data and 4 other correct pieces, it is
impossible (best I know anyway) to tell which
piece is the garbage piece.<br>
<br>
</div>
<div>One option in this case would be to seek
out an archival node that could verify the
correctness of the pieces, and identify the
malicious node.<br>
<br>
</div>
<div>Another option would be to have the small
nodes store a cryptographic checksum of each
piece. Obtaining the cryptographic checksum
for all 256 pieces would incur a nontrivial
amount of hashing (post segwit, as much as
100MB of extra hashing per block), and would
require an additional ~4kb of storage per
block. The hashing overhead here may be
prohibitive.<br>
<br>
</div>
<div>Another solution would be to find
additional pieces and brute-force combinations
of 5 until a working combination was
discovered. Though this sounds nasty, it
should take less than five seconds of
computation to find the working combination
given 5 correct pieces and 2 incorrect pieces.
This computation only needs to be performed
once to identify the malicious peers.<br>
<br>
</div>
<div>I also believe that alternative erasure
coding schemes exist which actually are able
to identify the bad pieces given sufficient
good pieces, however I don't know if they have
the same computational performance as the best
Reed-Solomon coding implementations.<br>
</div>
<br>
<div><b>Deployment:</b><br>
<br>
</div>
<div>Small nodes are completely useless unless
the critical mass of 5 pieces can be obtained.
The first version that supports small node
block downloads should default everyone to an
archival node (meaning indexes 0-4 are used)<br>
<br>
</div>
<div>Once there are enough small-node-enabled
archive nodes, the default can be switched so
that nodes only have a single index by
default. In the first few days, when there are
only a few small nodes, the
previously-deployed archival nodes can help
fill in the gaps, and the small nodes can be
useful for blockchain download right away.<br>
<br>
------------------------------<wbr>----<br>
<br>
</div>
<div>This represents a non-trivial amount of
code, but I believe that the result would be a
non-trivial increase in the percentage of
users running full nodes, and a healthier
overall network.<br>
</div>
</div>
<br>
</div>
</div>
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</blockquote>
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<br>
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<pre class="moz-signature" cols="72">--
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