NAND Flash Memory Garbage Collection Policy According to the Ratio of the Hot Pages

NAND flash memory is widely used as a storage device because of its features: low power consumption, high degree of integration, outstanding durability, and high access rates. Unlike hard disk, however, flash memory requires of garbage collection which consists of the copying and erasion operations and lowers the storage device performance. This study suggests a new garbage collection policy, aiming at reducing garbage collection overhead. The suggested garbage collection selects victim blocks in reference to the ratio of the hot page, and then reduces the number of copying and erasion by reducing the number of effective pages in the following GC operation. To evaluate the suggested method, a trace-driven simulation was conducted in comparison of the suggested method with the existing GC method. As a result, the performance was improved as much as 6~17% in terms of the number of copying and 4~20% in terms of the number of erasion. The total time of garbage collection was reduced as much as 9~28%, which proves the performance improvement.