Competition in the desktop NAS appliance market just keeps getting hotter with each vendor trying to outdo the others with an ever increasing features list. Thecus now goes another step beyond the rest as its latest N5500 five-bay appliance introduces the unique dual DOM feature, which targets businesses that want an extra level of fault tolerance.

So what is a dual DOM? In a nutshell, a DOM (Disk on Module) is a chunk of flash memory with an ATA, SATA or USB converter interface, which appears as a small hard disk to the host system. It can run an embedded operating system that’s used to boot the system. Thecus has used two 128MB Afaya IDE micro disk modules stacked on top of each other with the lower one plugged directly into the motherboard IDE interface. The idea here is that if one fails the other takes over.

In addition the N5500 supports NAS, DAS and IP SAN operations, supports more RAID types than you can shake a stick at and also introduces Thecus’ brand new Ajax based web interface. The latter is a much needed improvement with all features now much more accessible. We’ve always been distinctly unimpressed with the previous interface as it looks amateurish at best.

The N5500 offers a good general specification with a 1.86GHz Celeron M in the driving seat and partnered by 1GB of DDR2 memory. You get a quintet of USB 2.0 host ports, whilst a single USB 2.0 device port provides the DAS connection. There’s an eSATA port for expanding capacity with external drives and a pair of Gigabit ports, which support independent operations plus load balanced and failover teaming.

Installation is a swift process as Thecus’ Setup Wizard hunts down the appliance on the network, enabling you to change the admin password and network settings and provides quick access to the main web interface.

A pane to the left provides a tidy tree menu, whilst the main window alongside shows the relevant settings for your selections. You start by creating arrays and can choose from JBODs, mirrors, stripes, RAID-5 or dual-drive redundant RAID-6 and the appliance supports multiple arrays and array migration. We used a triplet of 1TB WD Greenpower SATA drives and a RAID-5 array took nearly five hours to build.

Pick your file systems carefully as although EXT3, XFS and ZFS are supported, volume snapshots can only be run on the latter, and this can only be accessed by CIFS/SMB users. At this stage you decide what percentage should be used for iSCSI targets and you can also create USB targets as well.

Client support is good as Windows, Linux, Unix and Mac systems are on the guest list. You also have FTP services, while access security extends to a local user database plus AD authentication. Businesses will find a modest range of backup options, which aren’t anywhere near as good as those offered by Netgear’s latest ReadyNAS appliances.

Thecus’ Nsync enables data to be copied from one appliance over the network to another to a schedule. The completely useless Backup Utility is still provided but the inclusion of FarStone’s DriveClone Pro is a smart move as it offers a lot more features. It secures selected files and folders on workstations at scheduled intervals, has a snapshot service for disaster recovery and offers drive and partition cloning as well.

The N5500 moved at a fair clip through our real world performance tests with copies of a 2.25GB video to and from a Broadberry dual 2.8GHz Xeon X5560 server returning average read and write speeds of 49Mb/sec and 41MB/sec. FTP speeds were slightly better with the FileZilla client utility reporting speeds of 51MB/sec and 43MB/sec.

iSCSI targets are easy enough to create as you decide on the amount of space, provide a name which is appended to the IQN and enable it. Performance was in the same ballpark as for general copy operations with our tests returning 50MB/sec read and 44MB/sec write speeds.

Thecus provides update modules for extra features but only the download station is currently available for the N5500 firmware. This is used by the appliance to retrieve remote files via BitTorrent, HTTP, FTP or eMule.



The Stackable feature is unusual as you declare iSCSI targets on other Thecus appliances that support IP SANs to the N5500, which can export them as network shares. We tried downloading and installing the IP camera module but this failed to work with the new firmware.

There is no user interaction possible with the dual DOMs as the appliance defaults to loading its OS from DOM1 and if this fails it’ll try the second. We tested this by physically separating the two DOMs and booting the appliance only with the primary device plugged in.

This worked fine but when we swapped it over with the secondary DOM we found that many of our configuration settings were missing. The RAID array was fine and had all our own folders and shares on it but a number of network services had stopped and all users, groups and AD settings were gone.

In the event of a boot failure the dual DOM will get essential storage back online but don’t bother using the configuration backup facility as this doesn’t include details of existing users and groups.

The N5500 certainly offers some unusual features and teams these up with a reasonable performance and a fresh new web interface. Business won’t be overly impressed with the backup features, which are easily bettered by Netgear’s ReadyNAS business appliances but the dual DOM isn’t a bad idea as it’ll get your storage back up in the event of a primary boot device failure.

Author: Dave Mitchell

Thecus N5500 review