The limited lifespan is the Achilles' heel of solid state drives(SSDs) based on NAND flash.NAND flash has two drawbacks that degrade SSDs' lifespan.One is the out-of-place update.Another is the sequential write constraint within a block.SSDs usually employ write buffer to extend their lifetime.However,existing write buffer schemes only pay attention to the first drawback,while neglect the second one.We propose a hetero-buffer architecture covering both aspects simultaneously.The hetero-buffer consists of two components,dynamic random access memory(DRAM) and the reorder area.DRAM endeavors to reduce write traffic as much as possible by pursuing a higher hit ratio(overcome the first drawback).The reorder area focuses on reordering write sequence(overcome the second drawback).Our hetero-buffer outperforms traditional write buffers because of two reasons.First,the DRAM can adopt existing superior cache replacement policy,thus achieves higher hit ratio.Second,the hetero-buffer reorders the write sequence,which has not been exploited by traditional write buffers.Besides the optimizations mentioned above,our hetero-buffer considers the work environment of write buffer,which is also neglected by traditional write buffers.By this way,the hetero-buffer is further improved.The performance is evaluated via trace-driven simulations.Experimental results show that,SSDs employing the hetero-buffer survive longer lifespan on most workloads.
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