Leveraging intra-page update diversity for mitigating write amplification in SSDs

Abstract

A solid state drive (SSD) receives requests in multiple of sectors from the host system, which are then mapped to logical pages, the basic I/O units of the flash memory. As the SSD receives requests in sector units, the sectors in a logical page tend to exhibit diverse update frequencies. Therefore, frequent updates to some sectors of a page cause other sectors of the same page to be unnecessarily read and written to other free pages, thereby increasing write amplification and harming the flash memory lifetime. To eliminate unnecessary sector movement and to reduce write amplification, we propose a sector-level classification (SLC) technique. SLC considers the diversity in the update frequencies of sectors and merges sectors with similar update frequencies to generate full, homogeneous pages. Thus, multiple update operations can be converged to a single flash page, thereby reducing write amplification and increasing flash memory lifetime. SLC handles the merged sectors using the proposed shared-page mapping table (SMT), whereas pages whose sectors remain unmerged are handled by a conventional page mapping table. Despite the SMT overhead, SLC does not require excessive resources to accommodate SMT. The capability of SLC is evaluated by a series of experiments, which provides highly encouraging results. It is demonstrated that SLC reduces flash writes, flash reads, block erasures, and flash writes execution time by 42%, 23%, 45%, and 37%, respectively.