Storage service apparatus with double controllers and high speed caching mirroring method

The invention provides a storage service device with dual controllers and a mirroring method of a cache thereof. The storage service device comprises an equivalent environment module, a storage device, a first controller and a second controller. The first controller is equipped with a virtual disk and a first cache. The second controller is equipped with a second cache. The method comprises the following steps: selecting the first controller or the second controller as a controller serving an external network by an equivalent environment way; writing the data which are received by the external network in the second cache if the controller selected by the equivalent environment way is the second controller; and establishing communication connection with the first controller, and writing the data which are received by the external network in the first cache and the virtual disk by the second controller.