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Summary: 12
Depot: Cloud Storage with Minimal Trust
PRINCE MAHAJAN, SRINATH SETTY, SANGMIN LEE, ALLEN CLEMENT,
LORENZO ALVISI, MIKE DAHLIN, and MICHAEL WALFISH, The University of Texas at Austin
This article describes the design, implementation, and evaluation of Depot, a cloud storage system that min-
imizes trust assumptions. Depot tolerates buggy or malicious behavior by any number of clients or servers,
yet it provides safety and liveness guarantees to correct clients. Depot provides these guarantees using a
two-layer architecture. First, Depot ensures that the updates observed by correct nodes are consistently
ordered under Fork-Join-Causal consistency (FJC). FJC is a slight weakening of causal consistency that can
be both safe and live despite faulty nodes. Second, Depot implements protocols that use this consistent or-
dering of updates to provide other desirable consistency, staleness, durability, and recovery properties. Our
evaluation suggests that the costs of these guarantees are modest and that Depot can tolerate faults and
maintain good availability, latency, overhead, and staleness even when significant faults occur.
Categories and Subject Descriptors: D.4.5 [Operating Systems]: Reliability--Fault-tolerance; D.4.7 [Op-
erating Systems]: Organization and Design--Distributed systems; C.2.4 [Computer-Communication
Networks]: Distributed Systems--Client/server; distributed systems; H.3.4 [Information Storage and
Retrieval]: Systems and Software--Distributed systems
General Terms: Design, Algorithms, Reliability, Experimentation, Security
Additional Key Words and Phrases: Cloud storage, Byzantine fault tolerance, Fork-Join-Causal (FJC)
consistency, fork consistency
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