Data storage apparatus

A storage system comprising:

• a first storage apparatus including a first data storage module having multiple areas, each of the multiple areas storing data;
• a second storage apparatus including a second data storage module having multiple areas, each of the multiple areas storing data;
• and
• a server to transmit a write command to the first and second storage apparatuses to perform data mirroring between the first and second data storage modules, the server including a controller to execute a process including:
• detecting that an abnormality occurs in the write command to the second storage apparatus,
• transmitting a first instruction of recording start for storing difference data between the first and second data storage modules, to the first storage apparatus, upon detecting the occurrence of the abnormality,
• receiving a completion-notice for the first instruction,
• retransmitting the write command, which is transmitted to the second storage apparatus when the abnormality occurs and until receiving the completion-notice from the occurrence of the abnormality, to the first storage apparatus, and
• transmitting a second instruction to restart performing data mirroring between the first and second data storage modules to the first storage apparatus when a restart instruction is input by an administrator,
• the first storage apparatus including
• a first memory to store bitmap information with a bit corresponding to each of the multiple areas in the first data storage area, and
• a first controller to execute a process including:
• receiving the first instruction from the server,
• creating the bitmap information with all bits having a first value, indicating that data stored in each of multiple areas in the first data storage module is identical to data stored in a corresponding area of the second multiple areas in the second storage module,
• transmitting the completion-notice to the server when creation of the bitmap-information is completed,
• receiving the write command from the server after transmitting the completion-notice to the server,
• storing data in the write command into an area, which is addressed by the write command, of the multi areas in the first data storage module,
• setting a second value indicating difference data between the first and second data storage modules to a bit in the bitmap information corresponding to the area addressed by the write command,
• receiving the second instruction from the server, and
• copying data stored in the area, which is corresponding to the bit having the second value in the bitmap information, of the multi areas of the first data storage module for data mirroring into a corresponding area of the second data storage module.