A Reliability Enhancement Mechanism for High-Assurance MLC Flash-Based Storage Systems

Solid State Devices (SDDs) are replacing mechanical data storage devices such as Hard Disk Drives (HDDs). On the other hand the data reliability in these systems is being questioned due to the fast growth in flash technology such as Multi-Level Cell (MLC). Recently it has been revealed that the Bit Error Rate (BER) increases exponentially in MLC flash memories as they experience more flash writes. Additionally RAID in flash-based storage systems has an inherent problem, that all flash devices should not reach end of life at the same time. Diff-RAID [2] overcomes the said problem. However, Diff-RAID mechanism suffers from drastic age-variation especially during the first few replacements, a problem that has been identified and addressed in this research. A new reliability enhancement mechanism for high-assurance MLC flash-based storage systems has been proposed here, and is compared with published Diff-RAID results. Our mechanism has shown promising results. In terms of convergence, the proposed scheme is 7 times faster. Furthermore, no single device crosses 66% of the age (i.e. max. erasure cycles), unlike the Diff-RAID where in the first few replacements, few devices reach 70-80% of age, which is great improvement in terms of data reliability.