Tasha Frankie, Gordon Hughes, and Kenneth Kreutz-Delgado
Solid state drives, write amplification, TRIM, NAND Flash
Write amplification is a major factor in the decrease in write speed which is observed in solid state drives (SSDs) as they fill with data. TRIM requests reduce write amplification by informing the SSD flash controller which data records are no longer necessary, and need not be copied during garbage collection. Models predicting the write amplification for workloads including TRIM requests can be used in real-world situations such as helping cloud storage data center operators manage resources to reduce costs without sacrificing performance and optimizing the performance of apps on mobile devices. In this paper, we modify formulas from Hu, et al., Agarwal, et al., and Xiang, et al. for computing write amplification under greedy garbage collection to account for TRIM requests, utilizing an analysis of effective overprovisioning allowed by TRIM. We then verify our results by simulation. Our theoretical (formula-based) prediction suggests, and our simulations verify, that a considerable write amplification reduction is found as the proportion of TRIM requests to Write requests increases. In particular, write amplification drops by almost half over the no-TRIM case if just 10% of requests are TRIM instead of Write.
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