This invention provides a storage system in which a volume containing WORM
data is restorable. A control unit, after the copying is finished,
consults a first meta data associated with data stored in a first block
of the first volume, consults, in a case where the consulted first meta
data including information indicating that the data stored in the first
block of the first volume is prohibited from being updated for a given
period, a meta data for a block that follows the first block of the first
volume, and restores, in a case where the consulted first meta data does
not includes information indicating that the data stored in the first
block of the first volume is prohibited from being updated for a given
period, data stored in the second volume into the first volume by copying
data stored in a second block, which is associated with the first block
of the volume, and is located in the second volume, to the first block of
the first volume, thereby reproducing the data of the second volume in
the first volume for restoration.