  We present CDStore, which disperses users' backup data across multiple clouds
and provides a unified multi-cloud storage solution with reliability, security,
and cost-efficiency guarantees. CDStore builds on an augmented secret sharing
scheme called convergent dispersal, which supports deduplication by using
deterministic content-derived hashes as inputs to secret sharing. We present
the design of CDStore, and in particular, describe how it combines convergent
dispersal with two-stage deduplication to achieve both bandwidth and storage
savings and be robust against side-channel attacks. We evaluate the performance
of our CDStore prototype using real-world workloads on LAN and commercial cloud
testbeds. Our cost analysis also demonstrates that CDStore achieves a monetary
cost saving of 70% over a baseline cloud storage solution using
state-of-the-art secret sharing.
