Patent ID: 7657719

Claim:
A controller that controls copying of data from a source medium to a destination medium, the destination medium having a logical storage capacity equivalent to that of the source medium and a physical storage capacity smaller than that of the source medium, an extracting unit that extracts data to be updated from an area containing the data within the source medium, wherein the data to be updated within the source medium are backed-up in the destination medium; and a copying unit that searches for a free space in the destination medium and copies the data extracted by the extracting unit from the source medium to the free space in the destination medium in such a manner as to copy the thus extracted data sequentially into an area beginning from a head address of the free space in the destination medium; wherein the controller further comprises: a first determining unit that determines, upon fetching a read request to read first data from the destination medium, whether the first data exists in the destination medium based on the logical to physical correspondence data; an acquiring unit that acquires, upon the first determining unit determining that the first data does not exist in the destination medium, the first data from the source medium and outputs retrieved first data; a second determining unit that determines, upon fetching an update request to update second data in the destination medium, whether the second data exists in the destination medium based on the logical to physical correspondence data; and an updating unit that copies, upon the second determining unit determining that the second data does not exist in the destination medium, the second data from a recording device in which the second data exists to the destination medium thereby updating contents of the destination medium.