A computer executes a data allocation control program to control allocation of data in a plurality of disk nodes. A redundancy restoration module executes a redundancy restoration procedure by commanding disk nodes to create a new copy of redundancy-lost data. An error message reception module receives a write error message indicating a write error in a storage device during the redundancy restoration procedure and records an identifier of the faulty storage device in an error record memory. A copy command module identifies accessed data in the faulty storage device and commands a relevant disk node to create a copy of the identified data in the faulty storage device in the case where there is no redundant copy of the data.