Architecting Data Placement in SSDs for Efficient Secure Deletion Implementation

摘要

Secure deletion ensures user privacy by permanently removing invalid data from the secondary storage. This process is particularly critical to solid state drives (SSDs) wherein invalid data are generated not only upon deleting a file but also upon updating a file of which the user is not aware. While previous secure deletion schemes are usually applied to all invalid data on the SSD, our observation is that in many cases security is not required for all files on the SSD. This paper proposes an efficient secure deletion scheme targeting only the invalid data of files marked as “secure” by the user. A security-aware data allocation strategy is designed, which separates secure and unsecure data at lower (block) level but mixes them at higher levels of SSD hierarchical organization. Block-level separation minimizes secure deletion cost, while higher-level mixing mitigates the adverse impact of secure deletion on SSD lifetime. A two-level block management scheme is further developed to scatter secure blocks over the SSD for wear leveling. Experiments on real-world benchmarks confirm the advantage of the proposed scheme in reducing secure deletion cost and improving SSD lifetime.