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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Tue, 12 May 2015 13:10:56 -0700
Message-ID: <CAJHLa0O3fgmg4AFAM9+4RRkhSo8ekATs2Ks+Ry7ooQafjQ-4qw@mail.gmail.com>
To: Gregory Maxwell <gmaxwell@gmail.com>
Content-Type: multipart/alternative; boundary=089e014954c8d1a48f0515e818f8
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Proposed additional options for pruned
	nodes
Precedence: list

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True.  Part of the issue rests on the block sync horizon/cliff.  There is a
value X which is the average number of blocks the 90th percentile of nodes
need in order to sync.  It is sufficient for the [semi-]pruned nodes to
keep X blocks, after which nodes must fall back to archive nodes for older
data.

There is simply far, far more demand for recent blocks, and the demand for
old blocks very rapidly falls off.

There was even a more radical suggestion years ago - refuse to sync if too
old (>2 weeks?), and force the user to download ancient data via torrent.


On Tue, May 12, 2015 at 1:02 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:

> On Tue, May 12, 2015 at 7:38 PM, Jeff Garzik <jgarzik@bitpay.com> wrote:
> > One general problem is that security is weakened when an attacker can
> DoS a
> > small part of the chain by DoS'ing a small number of nodes - yet the
> impact
> > is a network-wide DoS because nobody can complete a sync.
>
> It might be more interesting to think of that attack as a bandwidth
> exhaustion DOS attack on the archive nodes... if you can't get a copy
> without them, thats where you'll go.
>
> So the question arises: does the option make some nodes that would
> have been archive not be? Probably some-- but would it do so much that
> it would offset the gain of additional copies of the data when those
> attacks are not going no. I suspect not.
>
> It's also useful to give people incremental ways to participate even
> when they can't swollow the whole pill; or choose to provide the
> resource thats cheap for them to provide.  In particular, if there is
> only two kinds of full nodes-- archive and pruned; then the archive
> nodes take both a huge disk and bandwidth cost; where as if there are
> fractional then archives take low(er) bandwidth unless the fractionals
> get DOS attacked.
>


-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/

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<div dir=3D"ltr">True.=C2=A0 Part of the issue rests on the block sync hori=
zon/cliff.=C2=A0 There is a value X which is the average number of blocks t=
he 90th percentile of nodes need in order to sync.=C2=A0 It is sufficient f=
or the [semi-]pruned nodes to keep X blocks, after which nodes must fall ba=
ck to archive nodes for older data.<div><br></div><div>There is simply far,=
 far more demand for recent blocks, and the demand for old blocks very rapi=
dly falls off.<br><div><br></div><div>There was even a more radical suggest=
ion years ago - refuse to sync if too old (&gt;2 weeks?), and force the use=
r to download ancient data via torrent.</div><div><br></div><div><br></div>=
</div></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Tu=
e, May 12, 2015 at 1:02 PM, Gregory Maxwell <span dir=3D"ltr">&lt;<a href=
=3D"mailto:gmaxwell@gmail.com" target=3D"_blank">gmaxwell@gmail.com</a>&gt;=
</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .=
8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=3D"">On Tue, M=
ay 12, 2015 at 7:38 PM, Jeff Garzik &lt;<a href=3D"mailto:jgarzik@bitpay.co=
m">jgarzik@bitpay.com</a>&gt; wrote:<br>
&gt; One general problem is that security is weakened when an attacker can =
DoS a<br>
&gt; small part of the chain by DoS&#39;ing a small number of nodes - yet t=
he impact<br>
&gt; is a network-wide DoS because nobody can complete a sync.<br>
<br>
</span>It might be more interesting to think of that attack as a bandwidth<=
br>
exhaustion DOS attack on the archive nodes... if you can&#39;t get a copy<b=
r>
without them, thats where you&#39;ll go.<br>
<br>
So the question arises: does the option make some nodes that would<br>
have been archive not be? Probably some-- but would it do so much that<br>
it would offset the gain of additional copies of the data when those<br>
attacks are not going no. I suspect not.<br>
<br>
It&#39;s also useful to give people incremental ways to participate even<br=
>
when they can&#39;t swollow the whole pill; or choose to provide the<br>
resource thats cheap for them to provide.=C2=A0 In particular, if there is<=
br>
only two kinds of full nodes-- archive and pruned; then the archive<br>
nodes take both a huge disk and bandwidth cost; where as if there are<br>
fractional then archives take low(er) bandwidth unless the fractionals<br>
get DOS attacked.<br>
</blockquote></div><br><br clear=3D"all"><div><br></div>-- <br><div class=
=3D"gmail_signature">Jeff Garzik<br>Bitcoin core developer and open source =
evangelist<br>BitPay, Inc. =C2=A0 =C2=A0 =C2=A0<a href=3D"https://bitpay.co=
m/" target=3D"_blank">https://bitpay.com/</a></div>
</div>

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