Patent ID: 7162601

Claim:
A storage system coupled to a host computer via a network comprising: a data volume storing write data from the host computer; a snapshot storing area storing a first snapshot of at least a portion of the data volume at a first point in time and also storing a second snapshot of said at least a portion of the data volume at a second point in time subsequent to the first point in time; a journal storing area storing journal entries including a journal entry between the first point in time and the second point in time; and a storage controller to conduct write operations according to write requests received from the host computer and to manage snapshot operations to store a plurality of snapshots including the first snapshot and the second snapshot, wherein when receiving a data recovery request with a target time between the first point in time and the second point in time, the storage system selects the first snapshot based on the target time, selects at least one of the journal entries corresponding to the write operation conducted between the first point in time and the target time, and recovers data of the portion of the data volume at the target time by using the first snapshot and a portion of at least one of the journal entries selected, wherein the storage system manages journal operations to record the journal entries, monitors the journal storing area based on a predetermined criterion, and releases at least one of the stored journal entries prior to the second point in time when the predetermined criterion is met, and wherein the second snapshot is taken at the second point in time independently of when the at least one of the stored journal entries is released.