Thecus' N5810 Pro is the successor to the N4800, and the company's sole SMB NAS with a built-in mini-UPS battery backup system. For years, Thecus offered a single product with this capability for the small business and SOHO market. Every once in a while, it gets refreshed. The N5810 Pro is Thecus' best effort to date.
Power failures are harmful to storage products. I think it's safe to say that most of us have lost data due to a notebook running out of battery power or from a desktop shutting off unexpectedly during an electrical storm. Hard drives simply don't like losing power; it's not uncommon for them to come back online with a bad case of the click of death.
NAS products use several hard drives, so the chances of catastrophic failure multiply. If your drives do survive a power failure, then you have other issues to contend with. When power returns, the system scans the disks and attempts to repair any file system errors, bad blocks and so on. During that time, the transfer performance decreases and latency increases because the system is already performing background activities as fast as it can. With HDDs currently topping out at 10TB of capacity, it can take a long time to check the whole file system.
My family just went through a power fail event on a different NAS with twelve 6TB HDDs in RAID 6. The system is halfway full of data, so it took a long time to check everything. Since software RAID 6 consumes a lot of resources, the kids couldn't watch Blu-ray ISOs without the video skipping every few seconds. Even though the data was fairly safe thanks to redundancy, it wasn't truly available right away.
I've always wondered why Thecus is the only company with a battery backup-equipped product on the market. Most home users and small offices will not invest in a dedicated battery backup system. Building a UPS into the appliance is a step forward in the evolution of these products, and we would like to see the feature added to more products designed for home offices.
The N5810 Pro is also the first Thecus product we've tested with Btrfs (B-tree file system), a newer and more refined file system than Linux EXT4. Netgear rolled out Btrfs a year and a half ago with great success, and now Thecus offers it as an option alongside EXT3, EXT4 and XFS. Btrfs brings pooling, snapshots and checksums to the system.