Various methods for virtually realizing overwriting of data is adopted in write-once media that only allow sequential recording, such as DVD-R (Digital Versatile Disk), DVD+R and BD-R (Blu-ray Disc). This is because it is impossible to directly rewrite the data recorded on such media.
For example, according to the POW recording method, which is defined in the UDF (Universal Disk Format) Revision 2.60 standard and is applied to BD-R, a recording device realizes the virtual overwriting of data in the following manner. A recording device sequentially writes new data for the overwriting in the data area of a recording medium. That is, the recording device writes the new data at the tail of the existing data separately from the old data to be overwritten. The recording device stores substitution information, which shows the correspondence between the address of the area where the old data is recorded and the address of the area where the new data is recorded, into a POW information management area that is defined separately from the data recording area on the recording medium.
Meanwhile, since writing to and reading from recording media such as BD-R media is considerably slower than such processing performed on a memory, part of the memory area is often used as a disk cache.
As control methods used for recording of data stored in the disk cache onto the recording medium, there are a write through method and a write back method.
According to the write through method, when storing the data in the disk cache, the recording device also writes the data onto the recording medium. On the other hand, according to the write back method, the recording device firstly writes the data only in the disk cache, and writes the data onto the recording medium when, for example, the disk cache becomes full.
Since the required number of writing operations is smaller for the write back method than the write through method, the write back method is more suitable for the write-once media mentioned above.
For example, Patent Document 1 and Patent Document 2 each disclose technologies that use such a cache technique.    Patent Document 1: Japanese Laid-open Patent Application Publication No. 2002-91811    Patent Document 2: Japanese Laid-Open Patent Application Publication No. 5-257810
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