Information system and i/o processing method

An information system, comprising:

• a host computer;
• a first storage apparatus connected to the host computer and including a first volume designated by a volume identifier;
• a second storage apparatus connected to the host computer and including a second volume designated by the same said volume identifier as for the first volume;
• and
• a failure detection storage apparatus connected to the first storage apparatus and the second storage apparatus and including a third volume;
• wherein, for backup purposes, the first volume and the second volume form a remote copy pair, and write data to the first volume is copied to the second volume;
• wherein, for I/O request purposes, the first volume and the second volume are recognized in the information system as a single volume labeled with the same said volume identifier, but accessible by alternative access paths designated with differing priorities;
• wherein, a priority of a first access path from the host computer to the first volume is higher than a priority of a second access path from the host computer to the second volume;
• wherein, when the host computer sends an I/O request designating the same said volume identifier, the I/O request is first sent to the first volume through the first access path;
• wherein, when the I/O request sent to the first volume through the first access path ends in an error, the I/O request is then sent to the second volume through the second access path;
• wherein, upon receiving a write request sent from the host computer to the second volume through the second access path, the second storage apparatus suspends the remote copy, processes the write request and stores a write location of data recorded in the second volume based on the write request;
• wherein, if one of the first and the second storage apparatuses detects a failure in the other or a connection failure between the first and second storage apparatuses, the first or the second storage apparatus detecting the failure stores, in the third volume, a failure information flag showing that the failure was detected;
• wherein, upon receiving the I/O request through the second access path, the second storage apparatus determines whether the failure information flag is stored in the third volume, and sends an error reply of the I/O request to the host computer if the failure information flag is stored in the third volume.