[p2p-hackers] A Question about user awareness in p2p

[Sean C. Rhea]

On Mar 23, 2005, at 8:08 AM, Greg Bildson wrote:
> So, I guess the interesting followup question might be - does 
> OceanStore or Tapestry, etc, have any unique and easily communicable 
> insight into the
> issue of distributed long-term data storage.

Tapestry just stores pointers to data stored on other hosts.  The 
OceanStore model is exactly what you mention below: more stable hosts 
(possibly provided as part of a commercial infrastructure, possibly 
not) provide storage resources to the system.  On top of that, Hakim 
Weatherspoon has done some work on identifying sets of machines that 
are likely to be failure-independent, so that you don't 
replicate/erasure code a file onto a bunch of hosts that all fail at 
the same time.

One tricky part of all of this is accounting.  How do you know that the 
host that says it's storing your files is actually doing so without 
random sampling all the time?  The Samsara paper is the only published 
work I know of that looked at this right now.

> Or, do we really need a third class of network participant with closer 
> to
> server-like long uptime, perhaps a stable ip and able to dedicate a
> meaningful amount of storage.  In this latter case, I'm thinking about
> people dedicating a chunk of their linux(/web?) server to a network 
> that
> they believe in.

The other tricky part is consistency.  If you don't trust these hosts 
completely, you need something like a Byzantine agreement protocol.  
The actual protocols aren't too bad (although they're a little tricky 
to code), but mapping the files to hosts as they come and go and 
adjusting the protocol to handle those changes is hard.  More 
specifically, you have to handle the case where so much churn goes on 
that none of the original participants in the agreement group is around 
any more after some period of time.  I'm not aware of any published 
work on how to handle it.

Sean
-- 
   To announce that there must be no criticism of the president or that 
we
  are to stand by the president right or wrong is not only unpatriotic 
and
         servile but is morally treasonable to the American public.
                            -- Theodore Roosevelt

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