Gather Interface for Freezing Pages in Flash Storage

It is usual in many applications that a large fraction of data pages is, once created, actively updated for a while, and then eventually no longer updated. In flash storage, these frozen pages tend to spread over physical flash blocks and thus are repeatedly relocated upon garbage collection, exacerbating the write amplification. To address the problem of scattered frozen pages, we propose the interface, which allows users or applications to inform the flash storage of frozen pages explicitly. Upon receiving the call, FTL clusters and isolates frozen pages into a physically separate space so that they are no longer relocated upon garbage collection. Experimental results confirm that can reduce the write amplification factor from 25% to 40% of the conventional SSDs. The scheme is novel in the way it opens up a model case of physical tuning knobs in flash storage.