Synology FX2421 expansion units for Synology FlashStation make it easy to upgrade your all-flash storage space with Synology enterprise SSD. Each 2U rackmount unit lets you add 24 additional 2.5" drive bays on the fly using an expansion cable. Synology FX2421 24 bay expansion unit allows you to create a highly reliable and integrated storage setup, and receive long-term Synology updates and support.