The white paper “Two May be Better than One: Why Hard Disk Drives and Flash Belong Together” has been posted at http://www.snia.org/forums/sssi/knowledge/education/. The paper discusses the use of both solid state storage and HDDs in the same system. Specific mention is made of Paired Storage, a configuration where a small SSD allows fast boot up and quick access to frequently used files and the HDD provides high capacity at a low cost per GB.