GCMix: An Efficient Data Protection Scheme against the Paired Page Interference

Abstract

In multi-level cell (MLC) NAND flash memory, two logical pages are overlapped on a single physical page. Even after a logical page is programmed, the data can be corrupted if the programming of the coexisting logical page is interrupted. This phenomenon is called paired page interference. This article proposes a novel software technique to deal with the paired page interference without any additional hardware or extra page write. The proposed technique utilizes valid pages in the victim block during garbage collection (GC) as the backup against the interference, and pairs them with incoming pages written by the host. This approach eliminates undesirable page copy to backup pages against the interference. However, such a strategy has an adverse effect on the hot/cold separation policy, which is essential to improve the efficiency of GC. To limit the downside, we devise a metric to estimate the benefit of GCMix on-the-fly so that GCMix can be adaptively utilized only when the benefit outweighs the overhead. Evaluations using synthetic and real workloads show GCMix can effectively deal with the paired page interference, reducing the write amplification factor by up to 17.5% compared to the traditional technique, while providing comparable I/O performance.