Research On Performance Optimization Of Flash Memory Based On Refresh Technology

Nowadays,the share of flash memory composed of flash memory chips in the market is gradually increasing and has become a mainstream storage device.Due to the increase of flash memory density,the storage capacity of flash memory is larger and larger,and the price is lower and lower,which brings great convenience to personal storage and enterprise storage.However,the raw bit error rate(rber)of flash memory increases rapidly,the service life and data reliability of flash memory decline sharply,which has a major impact on data retention errors and read-write interference errors,and further reduces the performance of flash memory.Therefore,more flash memories use LDPC(low density parity check)error correction codes for error correction.LDPC can correct the data with high bit error rate to ensure the reliability of flash memory data,but its high error correction delay also has a certain impact on the reading performance of flash memory.Flash memory refresh technology can recover the wrong data through LDPC error correction code in idle time,which can effectively reduce the read delay and improve the data reliability.In this paper,two refresh schemes and a garbage collection scheme combined with refresh technology are proposed to improve the performance of flash memory,and the experimental verification is carried out on the disksim disk simulation system equipped with SSD module.(1)This paper proposes a hldb refresh scheme.The scheme judges the high LDPC delay block according to the LDPC decoding level,and reduces the LDPC decoding delay when reading the flash memory by refreshing the high delay block.Adaptive hldb scheme is the optimization of hldb scheme.This scheme distinguishes the high delay block judgment threshold in the early and late life of flash memory,which not only optimizes the read-write performance,but also reduces the loss of life.Experiments show that the average response time of hldb refresh scheme is reduced by 36.7%compared with FCR refresh scheme.Compared with the hldb refresh scheme,the adaptive hldb refresh scheme reduces the refresh times by up to 22.3%.(2)This paper proposes an HD refresh scheme,which refreshes the high delay pages in the state of hot read data with high accuracy on the basis of hot data recognition,optimizes the read-write performance of flash memory and improves the service life.The average response time of HD scheme is 25.3% lower than that of FCR refresh scheme and 46.6% lower than that of adaptive hldb refresh scheme.(3)This paper proposes a hldbgc scheme,which combines the hldb refresh function on the basis of garbage collection,so that garbage collection can not only create free blocks,but also improve the reliability and read-write performance of flash memory data.The average response time of hldbgc scheme is reduced by up to 7.2%compared with lagc scheme.These schemes based on refresh technology reduce the average response delay of flash memory and improve the service life to a certain extent.At the same time,they provide a new idea for the optimization of flash conversion layer of flash memory.