The Synology DS1520+ is a capable NAS for small offices or enthusiast users who need lots of storage space and the option to upgrade it further should if necessary. It uses the same CPU as the DS720+ and DS920+, but has more RAM, which can be expanded further by replacing the single DIMM with one of higher capacity. It also has four Gigabit Ethernet ports for faster network transfers if combined. Much better would have been 2.5 Gbit ports, and while none are available, the option to upgrade to 10 Gbit through a spare PCIe slot would have been better yet. The two NVMe slots, on the other hand, offer a great way to boost performance, especially IOPS.

Contrary to the DS1621+ I evaluated recently, RAM utilization is low during heavy utilization, but CPU utilization is high. The Intel Celeron J4125 is not that strong and struggles to keep up with the load since it doesn't have Hyper-Threading. That having been said, the Celeron CPU does include a UHD 600 graphics unit, while the V1500B doesn't have an embedded GPU, which puts it at a disadvantage for transcoding. The crucial advantage of the DS1621+ over the DS1520+ is the option for a 10 Gbit Ethernet card through a free PCIe slot and consequently higher network transfer speeds. With just $100 separating these models, the choice is not that tough. It depends on whether you need video transcoding or not. If you don't, the DS1621+ is the way to go. Otherwise, save $100 with the DS1520+, which is an excellent NAS.

The new DiskStation Manager (DSM) 7.0 operating system is a great improvement, especially for the GUI (Graphical User Interface). The previous version of DSM immediately felt old upon looking at the new GUI of the DSM 7.0. Besides its improved graphics design, it feels smoother and faster, and there are tons of other improvements as well. Storage Manager, an essential app, has been re-designed, offering increased usability. Besides being able to choose faster resync operations, you can now enable fast repair, which skips unused storage space to cut down on the time it takes for a degraded storage pool to be recovered. You can also remove the SSD cache without dismounting it first.

The control panel is permanently set to advanced mode since basic mode is not available, but who used basic mode anyway? Another significant change is that USB dongles are not supported anymore. Drivers that work in DSM 6.0 are no longer compatible, and for USB devices to work on DSM 7.0, the respective manufacturers have to develop new drivers. This means USB devices like Wi-Fi, Bluetooth, Cellular, DTV, and other adapters won't be compatible with the new OS, so you probably shouldn't upgrade yet if you need them. The same might be the case for some optional packages. So far, I can confirm that Plex Media Server works fine, and the same of course goes for all Synology-made apps.

EXT3 filesystem support has ended—if such volumes are in your NAS, transfer the data to volumes with supported file systems before upgrading. Another notable change is that Python3 has been merged into DSM as a built-in service, so you won't have to download the Python3 package from Package Center anymore. Some DDNS providers have been removed, and Insight & Hybrid Share Service are built-in services now. Through Active Insight, you have a centralized performance and status monitoring cloud service. Finally, Photo Station and Moments have been combined into Synology Photos.

To conclude, the DS1520+ is an excellent NAS for home users who can afford it, and the new DSM 7.0 OS is a massive improvement over the already very good DSM 6.2.4. Since this is a major upgrade, some problems are to be expected, like the slow write speeds in single-client scenarios, which will be fixed in future updates.