Synology 6,3 cm ( 2,5 inch ) Disk Holder provides an easy way for users to deploy 6,3 cm ( 2,5 inch ) HDDs on their disk stations. When 6,3 cm ( 2,5 inch ) HDDs are installed, the smart fan design keeps the Synology disk station fan off under normal operation. Under the circumstances the fan should spin up, it runs at a very low speed, thus provides library quietness, power saving, and higher reliability for the Synology disk station.