Tiered storage data evacuation within solid state devices

摘要

Exemplary methods and apparatus are disclosed to select data evacuation policies for use by a solid state device (SSD) to relocate data from an upper (high performance) memory tier to a lower memory tier. The upper tier may be, e.g., a single-layer cell (SLC) tier of a multi-tier NAND memory, whereas the lower tier may be, e.g., a triple-layer cell (TLC) or a quad-level cell (QLC) tier of the NAND memory. In one example, the SSD monitors its recent input/output (I/O) command history. If a most recent command was a read command, the SSD performs a “lazy” evacuation procedure to evacuate data from the upper tier storage area to the lower tier storage area. Otherwise, the SSD performs a “greedy” or “eager” evacuation procedure to evacuate the data from the upper tier to the lower tier. Other evacuation selection criteria are described herein based, e.g., upon predicting upcoming I/O commands.