External storage and data recovery method for external storage as well as program

A storage system to be connected to a host computer, comprising:

• a storage device which stores data to be used by the host computer;
• and
• a controller which controls the storage device,
• wherein the controller comprises:
• a memory which stores a recoverable point to be set by the host computer concerning data stored in the storage device, said recoverable point corresponding to journal data which includes journal control information having information necessary for recovering data on the storage device to the recoverable point and data size information indicating a size of write data corresponding to said journal data,
• wherein said controller sends information for selection related to the journal data at the recoverable point to the host computer in response to a request from the host computer, and recovers data designated by the host computer to a designated recoverable point based on the information for selection related to the journal data at the recoverable point,
• wherein the storage device includes a journal data area for storing journal data, and a backup data area for storing backup data,
• wherein, if a free space of the journal data area becomes insufficient, said controller transfers oldest journal data from the journal data area to the backup data area by an amount necessary to accommodate a size of the oldest journal data based on said data size information.

A storage system to be connected to a host computer, comprising:

• a storage device which stores data to be used by the host computer;
• and
• a controller which controls the storage device,
• wherein the controller comprises:
• a memory which stores a recoverable point to be sent by the host computer concerning data stored in the storage device, said recoverable point corresponding to journal data which includes journal control information having information necessary for recovering data on the storage device to the recoverable point and data size information indicating a size of a write data corresponding to the journal data,
• wherein said controller sends information for selection related to the journal data at the recoverable point to the host computer in response to a request from the host computer and recovers data designated by the host computer to a designated recoverable point based on the information for selection related to the journal data of the recoverable point,
• wherein the storage device includes a journal data area for storing journal data and a backup data area for storing backup data, and
• wherein, if a free space of the journal data area becomes insufficient, said controller searches for an unused area capable of storing the oldest journal data, extends a logical size of the journal data area to a capacity of the unused storage area and updates the journal control information based on the extended logical size of the journal data area.