THE EFFECT OF TRIM REQUESTS ON WRITE AMPLIFICATION IN SOLID STATE DRIVES

摘要

Write amplification is a major factor in the decrease inrnwrite speed which is observed in solid state drives (SSDs)rnas they fill with data. TRIM requests [1] reduce write amplificationrnby informing the SSD flash controller whichrndata records are no longer necessary, and need not berncopied during garbage collection. Models predicting thernwrite amplification for workloads including TRIM requestsrncan be used in real-world situations such as helping cloudrnstorage data center operators manage resources to reducerncosts without sacrificing performance and optimizing thernperformance of apps on mobile devices.rnIn this paper, we modify formulas from Hu, et al. [10,rn11], Agarwal, et al. [3], and Xiang, et al. [17] for computingrnwrite amplification under greedy garbage collection tornaccount for TRIM requests, utilizing an analysis of effectivernoverprovisioning allowed by TRIM [6, 7]. We thenrnverify our results by simulation. Our theoretical (formulabased)rnprediction suggests, and our simulations verify, thatrna considerable write amplification reduction is found as thernproportion of TRIM requests to Write requests increases.rnIn particular, write amplification drops by almost half overrnthe no-TRIM case if just 10% of requests are TRIM insteadrnof Write.