[M] Toshiba N300 4TB NAS Hard Drive Review
 

The newer SKUs of the N300 4TB drives do come with 256MB of cache (such as our sample) and coupled with a better hardware revision / newer firmware version the drive can deliver considerably better performance. The sequential read/write speeds are now higher with around 30MB/s, the drive featuring low noise during normal operation, but is no match in this regard for the helium-filled models which start from capacities of 12TB, that being a completely different price range!

http://www.madshrimps.be/articles/article/1001355/