The DS409slim has two USB ports (a connection via a USB hub is supported) and one eSATA connector for external devices such as storage devices, UPSes and printers. The NAS supports external storage with the FAT32, NTFS and EXT2/3 file systems. If there are multiple partitions on the hard disk, only the first of them will be accessible. The connected disk can be formatted from the NAS’s web-interface in FAT32 or EXT3.
Ordinary eSATA drives cannot be included into a RAID array. However, the DS409slim supports external DX5/RX4 enclosures for five and four disks, respectively (produced by Synology). HDDs installed in such enclosures can be fully integrated into the system.
The front USB port allows to copy data from the connected drive by pressing the dedicated button. The files are written into a subfolder named after the current data and time. The subfolder is created in a specified shared folder.
The UPS support is limited to shutting the NAS down in case of a power failure. You can choose the condition for that: waiting for the charge level to lower to a specific value, shutting down after a certain period of time, and shutting down immediately. An interesting feature available in the latest firmware is the emulation of a network UPS for five clients in which case you can use one UPS to power multiple NASes and shut them down all together when necessary.