BVSSD: build built-in versioning flash-based solid state drives

• Authors: Ping Huang;Ke Zhou;Hua Wang;Chun Hua Li
• Venue: Proceedings of the 5th Annual International Systems and Storage Conference
• Year: 2012

Time-traveling ability, which enables storage state to be reverted to any previous timepoints, is a highly desirable functionality in modern storage systems to ensure storage continuity. Continuous Data Protection (CDP) is a typical time-traveling implementation mechanism. CDP can guard well against software bugs, unintentional errors, malicious attacks, all of which are often beyond the capabilities of traditional periodical backup schemes. Broadly speaking, CDP can be implemented in two different ways, i.e., either integrate it seamlessly to the target file systems or more generally make it sit at the device block level. However, the state-of-the-art CDP implementations suffer from various limitations, e.g., huge implementation complexity, non-trivial performance interference. In this study, we introduce BVSSD, a new block level versioning system specifically designed for the emerging flash-based SSD. BVSSD realizes CDP functionality through positively and usefully exploiting the inherent idiosyncrasies of flash, which is the well-known "no-overwritten" property. Specifically, BVSSD simply keeps track of the SSD FTL metadata changes, which essentially represent the dynamics of the SSD storage state, and restores them to past timepoints to perform recoveries. Compared with existing block-level CDP schemes, BVSSD is much more light-weight, less performance-interfering, easier to realize, and more importantly, it requires no intrusive modifications to the upper file systems and applications. Our trace-driven simulation results with a number of different realistic enterprise-scale workload traces have shown that BVSSD only incurs marginal performance overheads, somewhere between 3% and 8% performance degradation, while with minimum additional RAM requirement, which is an acceptable price for the high reliability that BVSSD can provide. Furthermore, given most of the typcial SSDs deployment scenarios and their ever-increasing capacity trend, BVSSD is realistically poised to be feasible to be deployed in actual situations.