The Design and Implementation of a Fine-Grained Shielded Data Reduction System

Storage savings and data confidentiality are two primary yet conflicting goals in outsourced backup management. While deduplication-aware encryption has been extensively studied to make deduplication viable for encrypted data, it is incompatible with fine-grained delta and local compression for further storage savings. We present ShieldReduce, a secure outsourced storage system that aims for fine-grained shielded data reduction by applying deduplication, delta compression, and local compression to data in a trusted execution environment based on Intel SGX, so as to achieve high storage savings with security guarantees. To mitigate the I/Os of accessing base chunks for delta compression in SGX, ShieldReduce adopts bi-directional delta compression via a novel hybrid inline and offline compression design to maintain the physical locality of base chunks. It also offers a storage-prioritized offline compression mode for further storage savings and ensures crash consistency during data reduction. Evaluation on various backup workloads shows that ShieldReduce achieves significant speedups over a shielded baseline without bi-directional delta compression, while maintaining comparable storage savings to fine-grained data reduction for plain data.