Journal
ACM SIGPLAN NOTICES
Volume 53, Issue 6, Pages 44-54Publisher
ASSOC COMPUTING MACHINERY
DOI: 10.1145/3211332.3211338
Keywords
RAID; SSD arrays; Lifetime; Error-relaxation
Categories
Funding
- Research Grants Council of the Hong Kong Special Administrative Region, China [GRF 152223/15E, GRF 152736/16E, GRF 152066/17E]
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Flash-based SSD RAID arrays are increasingly being deployed in data centers. Compared with HDD arrays, SSD arrays drastically enhance storage density and I/O performance, and reduce power and rack space. Nevertheless, SSDs suffer aging issues. Though prior studies have been conducted to address this disadvantage, effective techniques of RAID/SSD controllers are urgently needed to extend the lifetime of SSD arrays. In this paper, we for the first time apply approximate storage via the interplay of RAID and SSD controllers to optimize the lifespan of SSD arrays. Our basic idea is to reuse faulty blocks (those contain pages with uncorrectable errors) to store approximate data (which can tolerate more errors). By relaxing the integrity of flash blocks, we observed that the endurance of NAND flash memory can be significantly boosted, thereby providing huge potentials to significantly extend the lifetime of SSDs. Based on this observation, we propose the use of an efficient space management scheme for data allocation and FTL strategies by coordinating the interplay of RAID and SSD controllers to optimize the lifetime of SSD arrays. We implemented a prototype, called FreeRAID, based on an SSD array simulator. Our experiments show that we can significantly increase the lifetime by up to 2.17x compared with conventional SSD-based RAID arrays.
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