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Modern peer-to-peer (P2P) storage systems have evolved to provide solutions
to a variety of burning storage problems. While the first generation
provided rather informal file sharing, more recent approaches provide more
extensive security, sharing, and archive capabilities.
To be considered a viable storage solution the system must exhibit high
availability and data persistence characteristics. In an attempt to provide
these, most systems assume a continuously connected and available
underlying communication infrastructure. But this is not necessarily the
case because equipment failures, denial of service attacks, and just poor
(yet common) corporate network design may cause discontinuities and
interruptions in the communication service. Any proposed storage solution
needs to address such issues transparently.
Storage archival systems can live with discontinuities, as long as the
stored data can be uniquely identified. Continuous update systems that
allow updating data by multiple writers have harder problems to overcome
since the ordering of updates needs to be maintained independently of
connectivity conditions. In this paper, we propose a solution for
maintaining the ordering even under severe connectivity disruptions,
allowing the system to continue functioning while connectivity is
disrupted, and to recover from the disruption smoothly when connectivity is
restored.
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