Method for rebalancing free disk space among network storages virtualized into a single file system view

A method for rebalancing unused capacities among network storage devices in a virtualized network storage system which includes a network coupled to the network storage devices, a virtualizing device which provides, to a client computer, a single storage device configured by the network storage devices, the method comprising the steps of:

• monitoring unused capacities of network storage devices of which unused capacity is smaller than a first predetermined value;
• comparing between a first unused capacity of a first network storage device among monitored network storage devices and a second unused capacity of a second network storage device among monitored network storage devices, the first unused capacity is smaller than a second predetermined value, the second unused capacity is biggest among the network storage devices;
• as a result of comparison, if difference between the first unused capacity and the second unused capacity is more than a third predetermined value, then, moving, via the network, one or more files from the first network storage device to the second file network storage device;
• judging whether the difference between the first unused capacity and the second unused capacity is smaller than the third predetermined value;
• if the difference between the first unused capacity and the second unused capacity is smaller than the third predetermined value, terminating the step of moving;
• and
• if the difference between the first unused capacity and the second unused capacity is larger than the third predetermined value, continuing the step of moving.