Design automation of Digital Microfluidic biochip (DMFB) is one of the active research topics in recent years. A couple of studies have been conducted to minimize the reservoir switching count, which significantly speeds up a multi-reactant mixing process. In general, it is easier to reduce the switching count if more on-chip storage units are available. Nevertheless, in reality, the number of storages is often limited due to the chip fabrication cost. Therefore, in this paper, we present a storage-aware scheduling algorithm for reservoir switching minimization. Experimental results demonstrate that the proposed algorithm can reduce the storage requirement by 44% while still achieving a 38% decrease in the reservoir switching count when compared with a state-of-the-art method.