Traditional RAID solutions (e.g., Linux MD) balance writes evenly across the array for high I/O parallelism and data reliability. This is built around the assumption that the underlying storage components are homogeneous, both in performance and capacity. However, SSDs, even for the same model, exhibit very different characteristics and degrade over time, leading to severe disk under-utilization. In this work, we present Asymmetric-RAID (Asym-RAID), a novel RAID architecture that optimizes system performance and storage utilization by exploiting heterogeneity from a larger SSD pool. Asym-RAID asymmetrically distributes data across the array to fully utilize the capacity of each SSD. To improve performance, Asym-RAID differentially exports the address space of each data stripe to the host, allowing for performance-optimized data placement. We outline the necessary changes in the storage stack for building an asymmetric RAID system and highlight its benefits.
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Reprogramming 3D TLC Flash Memory based Solid State Drives
NAND flash memory-based SSDs have been widely adopted. The scaling of SSD has evolved from plannar (2D) to 3D stacking. For reliability and other reasons, the technology node in 3D NAND SSD is larger than in 2D, but data density can be increased via increasing bit-per-cell. In this work, we develop a novel reprogramming scheme for TLCs in 3D NAND SSD, such that a cell can be programmed and reprogrammed several times before it is erased. Such reprogramming can improve the endurance of a cell and the speed of programming, and increase the amount of bits written in a cell per program/erase cycle, i.e., effective capacity. Our work is the first to perform a real 3D NAND SSD test to validate the feasibility of the reprogram operation. From the collected data, we derive the restrictions of performing reprogramming due to reliability challenges. Furthermore, a reprogrammable SSD (ReSSD) is designed to structure reprogram operations. ReSSD is evaluated in a case study in RAID 5 system (RSS-RAID). Experimental results show that RSS-RAID can improve the endurance by 35.7%, boost write performance by 15.9%, and increase effective capacity by 7.71%, with negligible overhead compared with conventional 3D SSD-based RAID 5 system.
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- PAR ID:
- 10316354
- Date Published:
- Journal Name:
- ACM Transactions on Storage
- Volume:
- 18
- Issue:
- 1
- ISSN:
- 1553-3077
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 2D memristors have demonstrated attractive resistive switching characteristics recently but also suffer from the reliability issue, which limits practical applications. Previous efforts on 2D memristors have primarily focused on exploring new material systems, while damage from the metallization step remains a practical concern for the reliability of 2D memristors. Here, the impact of metallization conditions and the thickness of MoS2films on the reliability and other device metrics of MoS2‐based memristors is carefully studied. The statistical electrical measurements show that the reliability can be improved to 92% for yield and improved by ≈16× for average DC cycling endurance in the devices by reducing the top electrode (TE) deposition rate and increasing the thickness of MoS2films. Intriguing convergence of switching voltages and resistance ratio is revealed by the statistical analysis of experimental switching cycles. An “effective switching layer” model compatible with both monolayer and few‐layer MoS2, is proposed to understand the reliability improvement related to the optimization of fabrication configuration and the convergence of switching metrics. The Monte Carlo simulations help illustrate the underlying physics of endurance failure associated with cluster formation and provide additional insight into endurance improvement with device fabrication optimization.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1145/3487064
