Patent ID: 7487293

Claim:
A data storage system, comprising: a plurality of disk storage devices which store data; and a plurality of control modules, connected to said plurality of disk storage devices, which control access to said disk storage devices according to access instructions from a higher-level system, each of said control modules comprising: a channel adapter performing an interface with said higher-level system; a disk adapter connected to said plurality of disk storage devices via a first line; a memory, having a cache area which stores a portion of the data stored by said disk storage devices; a control unit, which performs said access control; a pair of system disk units, connected to said control unit, which store at least log data of said control unit; and a system disk slot for inserting said system disk unit and connecting said inserted system disk unit to said control unit, wherein: one control module, upon occurrence of an abnormality in another of said control modules, detects that one system disk unit of said another control module has been inserted into said system disk slot of said one control module, incorporates said one system disk unit of said another control module, and outputs log data of said one system disk unit of said another control module; said channel adapter, said disk adapter and said pair of system disk unit are connected with said control unit; and said one control module, after incorporating said one system disk unit of said another control module, copies log data of the system disk unit of said one control module to said incorporated system disk unit, without destroying log data of said another control module on the system disk unit of said another control module.