Anandtech published 6 TB NAS Drives: WD Red, Seagate Enterprise Capacity and HGST Ultrastar He6 Face-Off A quote from the article:

Western Digital launched the first NAS-specific 6 TB drive today. In expanding their Red portfolio, they have brought 6 TB drives suitable for 24x7 operation into the hands of home consumers. Some enterprise-specific 6 TB drives have been around since late last year. Today's introduction provides us an opportunity to see how the WD Red compares against those offerings. Read on for our evaluation of the currently available 6 TB drives suitable for NAS units.

 6 TB NAS Drives: WD Red, Seagate Enterprise Capacity and HGST Ultrastar He6 Face-Off @ Anandtech