System for preventing duplication of autonomous distributed files, storage device unit, and data access method

A storage device unit included in an autonomous distributed type file system, comprising:

• a local storage;
• and
• a local controller,
• the local controller includes a storage directory and a duplicated data maintaining unit,
• wherein the storage directory has a function of keeping, in relation to data to be kept, an ID of a logical block and an ID of a physical block of the local storage of each of the storage device units, a value of a link to a node ID of a same or another storage device unit, and a value of a link to the logical block ID of this node ID, and
• wherein the duplicated data maintaining unit:
• refers to the storage directory,
• continuously keeps one real data item of the data and at least one replicated data item duplicately in a range without running out of storage capacity of the local storage, and
• restricts or prevents writing of the replicated data when there is no free space in the storage capacity.

A data access method for an autonomous distributed type file system,

• wherein the autonomous distributed type file system is a file system which has a plurality of servers, as a data reference device, which are connected through a plurality of access paths, and in which each of the access paths is connected to a plurality of storage device units,
• each of the storage device units includes a storage interface, a local controller, and a local storage,
• wherein the local controller includes a storage directory which is a table for managing writing or readout of data to or from the storage device unit of an own node, in accordance with free space in a capacity of the storage device unit, the method comprising the steps of:
• receiving a request for writing data from the server,
• referring to the storage directory, and continuously keeping one real data item of the data and at least one replicated data item duplicately in a range without running out of storage capacity of the own node, and
• restricting or preventing writing of the replicated data, when there is no free space in the storage capacity.