External storage device for storing update history

摘要

Embodiments of the invention provide an external storage system having a plurality of magnetic disk units which include a history storing device that automatically stores update information about the magnetic disk units as a history, and that can perform data recovery with a high degree of accuracy whenever a failure occurs. In one embodiment, an external storage system comprises a plurality of magnetic disk units being connected to one another according to a fiber channel protocol. At least one of the plurality of magnetic disk units is a history storing device that monitors each frame being transmitted to the plurality of magnetic disk units, and has an update history storing mode in which update history information is automatically obtained and stored in a storage medium of the history storing device.