There are not many NAS servers with dimensions as compact as the DS620slim, so the competition is thin. QNAP offers the high-end TVS-882ST3, mid-range TS-451S, and more budget-friendly TS-453B. However, I never had the opportunity to evaluate any of those, so I can't compare them properly with Synology's offer. I will also use SSD drives (thanks to the kind sponsorship from ADATA) instead of the slow HDDs I have been using so far from now on, which means I will lose fewer hours to testing, especially to the currently very lengthy RAID synchronization and build times.

The DS620slim performs very well in single-client scenarios and decently in the multi-client tests. I only noticed a drop in the tough six-client situation. With a stronger CPU, its performance could be improved in multi-client tests without affecting power consumption and noise output as the TDP would remain the same. The four-core Intel Celeron J3455 has the same 10 W TDP as the dual-core J3355 the DS620slim uses, for example.

Despite the small diameter cooling fan, output noise is kept very low. However, this may change with high-capacity mechanical drives since internal temperatures would increase significantly, which would make the fan spin at higher speeds to remove the heat. Even at its highest speed, though, which it never spun at throughout our testing period of two months, the small fan isn't that noisy because it doesn't exceed 38 dB(A) at a distance of a meter away.

The support for both EXT4 and btrfs is a tremendous advantage of the DSM operating system since it gives users the opportunity to select the for them more appropriate option. Synology recommends formatting the disks in btrfs. According to my tests, the performance difference is low, slightly in favor of the EXT4 filesystem. Another significant advantage of the DS620slim is that you can easily expand its memory to 6 GB if you decide to keep the stock 2 GB RAM module. If you replace it, you can reach up to 8 GB (2x 4 GB).

To conclude, I have to again complain about the lack of an HDMI port in a Synology review, which could transform this compact NAS into a great multimedia station. Adding a Thunderbolt 3 port would probably notably affect the production cost, but such is not the case with an HDMI port, so I cannot find any reason at all behind Synology's persistence on not providing this feature.