Backup and restoration for storage system

A system comprising:

• two or more storage media, each of the two or more storage media including a data part which is separated from an index;
• and
• a processor communicatively coupled to the two or more storage media, the processor being configured to perform a method comprising:
• migrating, to a second storage medium of the two or more storage media, a file within a file system for managing hierarchical storage, wherein the file includes a plurality of pieces of data, and wherein updated information is appended to and kept on the second storage medium;
• backing up metadata of the plurality of pieces of data to a first storage medium of the one or more storage media;
• backing up the index of the second storage medium to the first storage medium substantially at the same time point as backing up the metadata,
• wherein the index of the second storage medium includes location information for all files stored on the second storage medium, the location information including block numbers for each of the plurality of pieces of data,
• wherein a copy of the index is stored on the data part of the second storage medium, and
• wherein backup data of the metadata and the index is used in restoration along with the one or more storage media.