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Systems Seminar - CSE

Samsara: honor among thieves in peer-to-peer storage

Landon Cox
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Peer-to-peer storage systems assume that their users consume
resources in proportion to their contribution. Unfortunately, users
are unlikely to do this without some enforcement mechanism. Prior
solutions to this problem require centralized infrastructure,
constraints on data placement, or ongoing administrative costs. All
of these run counter to the design philosophy of peer-to-peer
systems.

Samsara enforces fairness in peer-to-peer storage systems
without requiring trusted third parties, symmetric storage
relationships, monetary payment, or certified identities. Each peer
that requests storage of another must agree to hold a claim
in return—a placeholder that accounts for available space. After an
exchange, each partner checks the other to ensure faithfulness.
Samsara punishes unresponsive nodes probabilistically.
Because objects are replicated, nodes with transient failures are
unlikely to suffer data loss, unlike those that are dishonest or
chronically unavailable. Claim storage overhead can be reduced when
necessary by forwarding among chains of nodes, and eliminated when
cycles are created. Forwarding chains increase the risk of exposure
to failure, but such risk is modest under reasonable assumptions of
utilization and simultaneous, persistent failure.

Paper available at http://mobility.eecs.umich.edu/samsara

Sponsored by

Brian Noble