STORAGE DEVICE

Logical hierarchies include an append hierarchy in a storage device. The storage device writes user data received in the append hierarchy to a free area, select a garbage collection operation mode for a first logical area in the append hierarchy from operation modes including first and second operation modes. Conditions of executing the garbage collection in the first operation mode include a capacity of the free area in the append hierarchy being less than a threshold, and an amount of garbage that is invalid data after update in the first logical area being equal to or greater than a threshold. Conditions of executing the garbage collection in the second operation mode include the amount of garbage in the first logical area being equal to or greater than a threshold value, while excluding the condition of the capacity of the free area in the append hierarchy.