At about half the size of the average two bay NAS enclosure, the four-bay Synology DiskStation DS411Slim is a great option when you need a lot of storage capacity (up to 6TB), but physical space is at a premium.
To achieve its compact form, the DS411slim simply uses bays designed for 2.5 inch drives (as opposed to 3.5 inch drives). But despite its diminutive size, this unit doesn’t lack for power, it's every bit as capable as any Synology box, which is saying a lot.
The slim in the DS411's name is actually a bit of a misnomer, it's small but not slim in any dimension. That said, it will fit in places the normal NAS box won't, and using 2.5 inch drives saves power.
It also has two USB 2.0 ports, one on the front next to the copy button so you can easily back up USB drives to the unit, and the other on back, directly underneath the eSATA connector. The drives slide easily out the back of the unit, which leads to my only complaint. It lacks a locking mechanism for the drives, which are relatively secure but held in place only by pressure.
Synology's windows-in-a-browser DiskManager Station 3.1 operating system is the current role model for the industry. Used on all its NAS enclosures, DSM is highly capable with features like iTunes and DLNA-certified media serving, email and website hosting, remote access via FTP, HTTP, FTPS, HTTPS and dedicated audio, photo and download interfaces.
Synology's NAS units are ideal small business servers, especially in light of their rsync syncing between NAS boxes. Set up two rsync-capable boxes in remote locations and they can mirror each other, amounting to offsite online backup without the yearly fees.
I tested the DS411slim with 2.5 inch, 500GB drives. Configured in a RAID 0 array, the unit averaged approximately 45MBps writing data to its drives, and about 58MBps reading from them during my hands-on tests on a gigabit network. That's quite fast (especially considering these were 5400rpm, 2.5 inch drives), and not much slower than Synology's DS211+.
Put simply, the DS411slim is a great little unit, emphasis on the words little and great.