Storage system and history information management method

A history information management method of a storage system including a storage controller, a plurality of volumes each comprised of the storage controller, and a pool configured to allocate physical storage areas to logical storage areas of the volumes, comprising the steps of:

• allowing the storage controller to include a first group including, among the volumes, at least one first primary volume to which a first target protection period is set, a first copying volume storing a copy of the first primary volume at a predetermined time, and a first history information volume storing history information about updating to the first primary volume, and a second group including, among the volumes, at least one second primary volume to which a second target protection period is set, a second copying volume storing a copy of the second primary volume at a predetermined time, and a second history information volume storing history information about updating to the second primary volume;
• allowing the volumes included in the first group and the second group to utilize the same physical storage area of the pool;
• and
• when a free capacity of the pool is increased from a state in which the history information about the updating to the first primary volume, which is stored in the first history information volume is capable of providing the first target protection period and a first protectable period, and the history information about the updating to the second primary volume, which is stored in the second history information volume is capable of providing a second protectable period equivalent to a period longer than the second target protection period, determining the history information to be purged from the first protectable period and the second protectable period in such a manner that the first protectable period and the second protectable period are put in a predetermined relation.