Synology Disk Holder (Type C) 3.5in to 2.5in SSD/HDD Adapter for Synology NAS Units Synology 2.5" Type C Disk Holder provides an easy way for users to deploy 2.5" HDDs or SSDs on their Synology NAS. When 2.5" HDDs are installed, Synology NAS can provide further library quietness, power savings, and higher reliability when compared to 3.5" HDD counterparts.