Emulation technique for variable-length disk system to access data in a fixed-length disk system

A method of controlling a disk in a disk system that includes a disk control unit connected to an upper system that uses a variable-length formatted disk and emulating said variable-length formatted disk with the use of a fixed-length formatted disk and including a cache, said variable-length formatted disk employing as an access unit a variable-length record that includes a format information area and a data area, said fixed-length formatted disk employing a block as an access unit, and a fixed-length formatted disk unit controlled by said disk control unit, comprising the steps of:

• setting a format information area storing region and a data area storing region in said fixed-length formatted disk unit, said format information area storing region collectively storing said format information areas of each variable-length record, said data area storing region being separated from said format information area storing region and storing remaining data that remain in each variable-length record other than said format information area;
• in said disk control unit, in response to a writing access into said variable-length record from said upper system, dividing from said variable-length record, said format information area existing in each variable-length record, and
• collectively storing said divided format information areas into said format information area storing region in said disk unit.