In recent years, the physical capacity of storage has been increasing due to refinement and densification; however, error rates have been increasing with the increase in capacity, and the lifespan of storage is becoming shorter. In order to compensate for this, for example, it is necessary to take countermeasures such as error correction and redundancy, and it is becoming difficult to increase the capacity that can actually be used.
Furthermore, in conventional storage, when reading or writing, it is not possible to know what kinds of data are going to be read or written and to what extent these are going to be read or written, and it is therefore necessary to take the worst values for all cases into consideration in the design concerning performance and quality assurance and so forth.
Furthermore, a technology has also been proposed that uses both the two systems of the MLC system and the SLC system as systems for recording data, and also changes the recording system in accordance with the type of recording data, such as whether or not the recording data is file system data (for example, see Patent Document 1). An SLC (single-level cell) is a system for recording 1 bit of data in one cell, and an MLC (multi-level cell) is a system for recording a plurality of bits of data in one cell. In this case, the SLC system is employed in portions having a high update frequency such as the FAT. Thus, it is possible to realize an increase in recording capacity, and to prolong the memory lifespan.
In addition, mixing storage devices that have a low power consumption but also have a low write performance and a short device lifespan, suitably controlling those plurality of storage hierarchies, allocating the storage hierarchies corresponding to a policy designated with respect to the attributes and volume of data, and thereby realizing storage having low power consumption and little decline in performance has also been proposed (for example, see Patent Document 2). In this technology, parameters that affect lifespan, such as the number of times writing is performed to a device and the number of times erasing is performed, and the power consumption in devices are managed, and the transition between the storage hierarchies is suitably controlled.