Research On Optimizing Read-Retry Algorithm Of Solid State Drives

Recently,solid state drive(SSD)manufacturers reduce production cost by utilizing advanced storage technologies such as multi-layer cells.Though these technologies can increase the storage density,continuously reduce the data reliability of SSD.Faced with increasingly serious reliability problems,SSD with read retry mechanism resolves uncorrectable data errors of error correction code.The read retry methods consist of multiple retry steps that will adjust the read reference voltage to repeatedly read data,until error correction code can correct data errors.Read retry method has little space overhead,but introduces more serious read disturbance and significantly increases the read request response time of the SSD.To improve the performance of existing read retry method in SSD,an adaptive fast read retry algorithm is proposed.The adaptive fast read retry algorithm utilizes two characteristics that retry steps number is various under different flash states and different access frequency of various logical addresses,which optimizes the performance of the existing read retry algorithm.Firstly,in the list of retry counts of flash memory chips,the minimum retry counts is determined by program/erase counts and retention time of the flash block.Then,the correction operation in some retry steps is skipped with the minimum retry counts,and next retry step is performed immediately to avoid unnecessary correction operations.Finally,the read request hotness is determined by counting the access frequency of logical addresses.Fast read retry algorithm and pipeline read retry algorithm are executed for hot request and cold request respectively,which further reduces the read request response time and the number of read refresh.The experimental results on the Microsoft Cambridge Research traces show that compared with pipeline read retry algorithm,the adaptive fast read retry algorithm reduces the number of read refresh by an average of 24.1% and reduces the read response time by4.4% on different traces;Compared with regular read retry,adaptive fast read retry can reduce the read response time by 19.1%.Experiments show that the adaptive fast read retry algorithm can effectively reduce the number of read refresh,reduce the read response time,and optimize the read performance of the SSD.