I. Introduction
The amount of digital data produced by humans is increasing every day. Based on the IDC report [1], the amount of information and content created and stored digitally will grow to over 7 zettabytes by 2015. This explosion of digital data must be managed and used with data intensive applications such as sensor data archives, search engines, and customer management systems (OLTP). As well, the increased data must be stored somewhere, which implies that storage capacity must also increase. The report [2] says that the storage capacity shipment in 2014 will be 7 times as large as that in 2009.