Qnap’s TS-451DeU will appeal to small offices with limited space as it’s one the shortest NAS appliances we’ve yet seen. Presented in a chassis that’s a mere 11.6 inches deep, it can be easily fitted in a small wall box, a standard two-post rack cabinet or even placed on a desk.
This shortness doesn’t come at the cost of features as it’s equipped with dual 2.5GbE multi-Gigabit network ports which offer a network boost beyond 1GbE using your existing Cat5e/6 cabling. It also has a pair of M.2 SSD slots inside that can be used as a high-speed storage pool, a disk cache or a performance tier for Qnap’s Qtier 2 data migration feature.
The appliance is powered by a dual-core 2GHz Celeron J4025 CPU teamed up with 2GB of DDR4 memory. The appliance has two SO-DIMM slots so you can boost capacity to 6GB without losing the standard module.
Pairs of USB 3.2 Gen 1 and USB 2 ports are provided at the rear which can be used to attach up to two of Qnap’s USB expansion enclosures. There are plenty to choose from with the 4-bay TR-004U enclosure looking the best partner for the TS-451DeU as its 1U chassis is even shorter.
TS-451DeU Build quality and deployment
The appliance is clothed in a solid steel chassis and uses equally sturdy metal carriers which have screw holes provided for LFF and SFF disks. For testing, we had no problems fitting a triplet of 16TB Seagate IronWolf NAS drives.
The appliance uses an internal power supply and cooling is handled by three small fans arranged along the rear panel. Noise levels are very low as using the SPLnFFT app on an iPad, we recorded a whisper-quiet 38dB at one meter in front.
The lid is secured with five screws and underneath you’ll find a tidy interior offering easy access to the memory and M.2 SSD slots. For cache testing, we slotted in two 256GB SSDs and fitted them with the little metal heatsinks provided in the appliance’s accessory box.
Installation is a cinch as the QFinder Pro Windows app discovered the appliance on the lab network and directed us over to its web interface where a quick start wizard installed the current production QTS software.
Once it had completed, we used the Storage & Snapshots app to create a big 32TB RAID5 array from our Seagate drives.
Qfinder Pro offers a number of other useful features as its Storage Plug and Connect option streamlines setting up and mapping NAS shares or creating, discovering and connecting to iSCSI targets. It provides direct access to shares via Windows Explorer or an FTP session, controls for remotely rebooting or powering off the appliance and a handy media upload tool.
2.5GbE and cache performance of the TS-451DeU
For NAS performance testing, we hooked the appliance up to a Netgear MS510TX multi-Gigabit switch. For our host, used a Dell EMC PowerEdge T640 Xeon Scalable tower server running Windows Server 2019 and connected to the switch’s 10GbE port.

The appliance’s dual M.2 SSD slots can be used as a performance boosting cache for random write operations
With a NAS share mapped to the server, we saw Iometer report excellent sequential read and write rates both of 2.3Gbits/sec. These translated to top real world speeds with our 25GB drag and drop file copies returning read and write averages of 2.3Gbits/sec and 2.2Gbits/sec.”’
Backup performance was reasonable as securing a 22.4GB folder with 10,500 small files to the share averaged 1Gbits/sec. The Celeron’s integral AES-NI engine proved to be very efficient as copying our 25GB test file to an encrypted share returned a respectable 1.3Gbits/sec.
IP SAN performance is good with a 1TB target returning Iometer read and write rates of 2.3Gbits/sec and 2.2Gbits/sec. With a dual 2.5GbE MPIO iSCSI link to the target, we watched read and write performance ramp up nicely to 4.4Gbits/sec and 3.8Gbits/sec.
If you’re planning on using an M.2 SSD cache, you will only see significant improvement with apps that use random write operations – such as databases and photo indexing tasks. Using our dual 2.5GbE MPIO link, we recorded Iometer random write speeds of 0.23Gbits/sec and a throughput of 201 IOPS which a mirrored read/write cache boosted significantly to 1.6Gbits/sec and 10,500 IOPS
QTS app choices
With Intel in the driving seat, the TS-451DeU can run any app the QTS software has to offer. Qnap is aiming the TS-451DeU firmly at SMB data protection duties and in this area you’re spoilt for choice with services ranging from scheduled NAS and IP SAN snapshots to on-appliance data backup, synchronization and replication.

Qnap’s free NetBak Replicator software provides plenty of workstation and server backup and recovery tools
The 2.5GbE ports deliver more bandwidth for workstation backup and Qnap provides the free NetBak Replicator utility which can be installed on an unlimited number of Windows desktops and servers. It’s easy to use as you choose a share on discovered Qnap appliances to send your data to and pick from auto-backup for continuous protection, scheduled backup or instant backup of selected drives, folders and files.
Other standout business apps include Qnap’s Hybrid Backup Sync (HBS) 3 app for automated backup and deduplication of appliance data plus Hyper Data Protector for securing virtual machines on VMware and Hyper-V hosts. Qnap is a great choice if you want to bring cloud storage into the network equation as the HybridMount app allows you to mount storage from a range of cloud providers as NAS shares and assign a local cache to them.
The TS-451DeU is ideal as a discrete IP camera monitoring and recording solution with the free version of Qnap’s QVR Pro app including an 8-channel license and supporting 14 days of video playback. You can purchase camera extension licenses up to a maximum of 128 channels and Qnap now offers an unlimited playback license which costs around $130.
Conclusion
Space poor SMBs will love Qnap’s TS-451DeU as it’s one of the most compact 1U rack mount NAS appliances on the market. It lacks an expansion slot and heavy hitters will want to upgrade the basic 2GB of memory but this slim-line NAS scores well for its dual multi-Gigabit ports, M.2 SSD slots, feature-rich QTS software, good 2.5GbE performance and very reasonable price tag.