The DS409slim is going to be appreciated by users who prefer compact electronic devices. Although it can accommodate as many as four HDDs, its size is very small. Why? Because it uses 2.5-inch rather than 3.5-inch HDDs. This has not affected functionality. The DS409slim is a very capable NAS like any other model from Synology. We have not noticed any differences in terms of speed, either.
Thus, the single serious downside of the 2.5-inch NAS is that its storage capacity is smaller in comparison with 3.5-inch models. External drives with USB or eSATA interface can but partially mitigate the issue.
This pretty and interesting thing comes at a rather steep price of over $500 but you must be aware that it’s impossible to build a system of a comparable size out of standard components. So, if you need a very small but high-capacity and highly functional NAS for storing your valuable data, this model will make a good buy.