An information processing system, comprising: a first server apparatus which comprises a first file system and which is configured to receive I/O requests from a client apparatus; a first storage apparatus which comprises storage of the first server apparatus; a second server apparatus which comprises a second file system and is communicably connected to the first server apparatus; and a second storage apparatus which comprises storage of the second server apparatus; wherein the first server apparatus is configured to transmit data of a file which is the target of the I/O request and which is stored in the first storage apparatus to the second server apparatus, and the second server apparatus is configured to store the data which is sent from the first server apparatus in the second storage apparatus while holding a directory image of the first file system in the second file system, wherein the second server apparatus is configured to acquire a first directory image of a predetermined level in the directory image that is configured in the file system of the first server apparatus from the directory image in the second storage apparatus and to transmit the first directory image to the first server apparatus, the first server apparatus is configured to, upon receiving an I/O request for a file which is to be restored from the client apparatus after the first directory image sent from the second server apparatus is restored to the first storage apparatus, determine whether or not a second directory image which is required to process the received I/O request exists in the first directory image of the first storage apparatus and, if the second directory image does not exist, issue a request to the second server apparatus to request the second directory image, the second server apparatus is configured to, when the request is sent from the first server apparatus, read the second directory image from the second storage apparatus and transmit the second directory image to the first server apparatus, and the first server apparatus is configured to restore the second directory image to the first storage apparatus, the first server apparatus is configured to restore an object directory image, which includes the first directory image and the second directory image, to the first storage apparatus, and the second file system of the second server apparatus is configured to, whenever a file system object is created or updated, manage the created or updated file system object using a different version ID, and the first server apparatus is configured to utilize the version ID in the process of restoring the object directory. a first server apparatus which comprises a first file system and which is configured to receive I/O requests from a client apparatus; a first storage apparatus which comprises storage of the first server apparatus; a second server apparatus which comprises a second file system and is communicably connected to the first server apparatus; and a second storage apparatus which comprises storage of the second server apparatus; wherein the first server apparatus is configured to transmit data of a file which is the target of the I/O request and which is stored in the first storage apparatus to the second server apparatus, and the second server apparatus is configured to store the data which is sent from the first server apparatus in the second storage apparatus while holding a directory image of the first file system in the second file system, the second server apparatus is configured to acquire a first directory image of a predetermined level in the directory image that is configured in the file system of the first server apparatus from the directory image in the second storage apparatus and to transmit the first directory image to the first server apparatus, the first server apparatus is configured to, upon receiving an I/O request for a file which is to be restored from the client apparatus after the first directory image sent from the second server apparatus is restored to the first storage apparatus, determine whether or not a second directory image which is required to process the received I/O request exists in the first directory image of the first storage apparatus and, if the second directory image does not exist, issue a request to the second server apparatus to request the second directory image, the second server apparatus is configured to, when the request is sent from the first server apparatus, read the second directory image from the second storage apparatus and transmit the second directory image to the first server apparatus, and the first server apparatus is configured to restore the second directory image to the first storage apparatus, the first server apparatus is configured to restore an object directory image, which includes the first directory image and the second directory image, to the first storage apparatus, and the second file system of the second server apparatus is configured to, whenever a file system object is created or updated, manage the created or updated file system object using a different version ID, and the first server apparatus is configured to utilize the version ID in the process of restoring the object directory.