Thecus N5550 review

The Thecus N5550 is a standalone NAS enclosure with an Intel Atom D2550 processor, 2GB of RAM and the capacity to take up to five hard disks, which means it’ll support RAID5 arrays with a hot spare, a feature lacking from many smaller NAS devices.

It has a mono LCD status screen at the bottom that displays errors, the NAS’s IP address and other useful information. It also has a single USB3 port at the front, as well as four USB ports, one eSATA port and HDMI and VGA ports at the rear. This means you can connect a monitor directly. You can also control the N5550 with a USB keyboard and mouse instead of using a network-connected PC. You must install the local display module to do this, but it’s a free download of almost 400MB.

The N5550 supports the usual range of JBOD, RAID0, RAID1, standard RAID5, RAID6 and RAID10, although it defaults to RAID6 and the ext4 file system. RAID6 has some significant advantages over RAID5 when it comes to minimising wear on disks. If one your drives fails and the others are of the same age and brand, the stress of rebuilding the RAID5 array can be enough to take down your remaining drives. RAID6 has its disadvantages, though. It requires two entire redundant drives, versus RAID5’s single redundant disk, and it also has slower write speeds due to the way it arranges its data on the disks. This particularly affects tasks that write thousands of very small files to disk.

We tested the NAS using a matched set of four 3TB Western Digital Red hard disks. For our initial test, we used the N5550’s default RAID6 configuration and mounted a directory on the NAS as an SMB share. In our large file transfer test, this produced an average transfer speed of 83.2MB/s (101.5MB/s read, 64.1MB/s write). When we got to our more challenging small file transfer test, files wrote at 14.4MB/s and read at 17.9MB/s, producing an average of 16.2MB/s.

For comparative purposes, we reconfigured our drives as a RAID5 array, created an SMB share and ran the same tests. This time we saw transfer speeds of 92MB/s when writing and 73.5MB/s when reading large files, and 13.5MB/s when writing and 17MB/s when reading small files. Although the chances of drive failure at RAID5 are still very low, you probably better off with RAID6.

For our next test we created a RAID5 iSCSI target instead of an SMB share. An iSCSI LUN is a logical device. It’s a portion of space on your NAS that your PC can address as if it’s a local hard drive. This allows faster access speeds because your PC is responsible for more of the processing load rather than the NAS. Windows has a built-in iSCSI Initiator program that makes it easy to attach a NAS-based iSCSI target to your PC so you can format it and generally treat it just like a standard hard disk. This is one of the fastest and most efficient ways of using a NAS device for data storage. We found it easier to set up iSCSI targets on Synology and QNAP devices than the N5550. When we ran our speed tests on an N5550-based iSCSI, we got average speeds of 98.2MB/s for large files and 32.2MB/s for small files. Using a RAID6 configuration, we got 91.5MB/s and 28.8MB/s in large and small file tests respectively.