You say it's an NAS drive, which implies you either bought something marketed as a complete NAS solution (in which case it's badly broken, and should be returned) or you put a bare drive in some sort of enclosure. If the latter, then the problem is almost certainly that the enclosure has a 32-bit addressing limit. This usually causes disk capacity to "wrap," sort of like the odometer on an old car. In a car with a 5-digit odometer, once you hit 99,999 miles (or kilometers), the odometer "wraps around" and shows a mileage of 0 when the car really has 100,000 miles on it. When the car has a true mileage of 150,000 miles, the odometer reads 50,000, and so on. Something analogous happens on devices with 32-bit limitations, but the wrap point is typically 2 TiB, then again at 4 TiB, 6 TiB, and 8 TiB. What you're seeing is therefore the part of the disk's capacity above 8 TiB. (Note that TB is not the same as TiB; TB is smaller than TiB, so you're not seeing a full 2 TB, much less 2 TiB, between 8 TiB and 10 TB.)
This sort of problem is extremely common with USB enclosures. You identified the disk as an NAS device. I'm not all that familiar with this type of device, but my understanding is that these are file-level servers; but your output identifies the disk as
/dev/sdb, which is not how I'd expect a true NAS to appear -- unless you've shown the NAS device's kernel output. Thus, I am a little bit confused. You may want to clarify matters by identifying the exact products involved and from where you're getting that kernel output -- on your Ubuntu computer or on the NAS.
In any event, there are several possible solutions:
- Direct connection -- You can connect the disk directly to the computer's motherboard, rather than via your external enclosure. It's very rare to have such problems in Linux with disks that connect directly via a SATA port. (Windows users aren't so lucky; there are Windows drivers with 32-bit limits.)
- Reconfigure the enclosure -- Some enclosures have switches that can adjust how they treat the disk. These usually enable a "translation" of eight 512-byte sectors into single 4096-byte sectors, thus raising the 2 TiB limit to 16 TiB. This is big enough to handle your 10 TB disk. (You should be aware that this change will invalidate existing partition definitions, though, so do this only if you have not already partitioned the disk and stored data on it.)
- Change the interface method -- Some USB enclosures also sport eSATA ports. Using eSATA normally works around the problem.
- Get a new enclosure -- If all else fails, you can often fix the problem by buying a new enclosure. If my suspicion that you're using a USB enclosure is correct, you can either get one that does the sector-size translation I've just described to boost the capacity to 16 TiB or you can switch to an enclosure with a different type of interface, like eSATA or a true NAS that partitions the disk itself and communicates over Ethernet using NFS, SMB/CIFS, or some other higher-level protocol.