We propose a data migration method for widely distributed autonomous disks, in which user?s frequently accessed and important data are automatically transferred to the nearest disk and/or duplicated to others by using ECA rules, according to the properties of the data. Recently, a mobile user can handle a large amount of data because mobile disks are installed on many gadgets. However, data required by a user are not always on his mobile disk. Even if they are on it, the reliability is low due to the possibility of a disk crash. The proposed system makes use of multiple sets of ECA rules on autonomous disks and chooses an appropriate rule set in response to the changes of system states, so that optimal data accesses can be performed by migrating and/or duplicating the data to other disks. This system could bring comfortable and reliable data accesses to mobile users.