Disk cache system

Claim 1

A disk cache system comprising; a host processor; a disk unit; and a disk controller interposed therebetween and incorporating therein a disk cache buffer, said disk controller having a cache directory for controlling said disk cache buffer in units of blocks of a predetermined size and having write flags in respective entries, an error log table in which error status information is set, an extent table having entries in which file extent information is set, first means, responsive to a first command generated from the host processor and having file extent information defining a file area, for setting the file extent information in the extent table and for securing a corresponding area in said disk cache buffer, second means, responsive to a second command generated from said host processor and requesting write into said disk unit, for storing data into the corresponding area of said disk cache buffer and for setting the write flag of a corresponding entry of said cache directory, third means for writing into said disk unit data in said disk cache buffer which has not been written in said disk unit utilizing an idle time of input/output processing using said disk cache buffer and for resetting the write flag of the corresponding entry of said cache directory, fourth means, responsive to a third command generated from said host processor, having the file extent information, and designating a logical termination unit of a program, for writing into said disk unit data corresponding to a file area represented by the file extent information in said third command and for resetting the write flag of the entry of said cache directory, said data being selected from the data in said disk cache buffer which has not been written in said disk unit, fifth means, when an error is generated during data write into said disk unit, for setting the error status information into said error log table such that said error status information corresponds to the file extent information stored in said extent table and defining file areas including an area in which the data is to be written, and sixth means, upon being initiated after termination of a control operation of said fourth means, for selectively fetching from the error log table the error status information corresponding to the file extent information in the third command and transferring the error status information to said host processor.