When the R710 was released, 2TB was the largest supported, and 3TB were not common. The first firmware update added support for >2TB drives on the H700 controller. The PERC 6 has a HARD limit of 2TB per physical disk. So, to answer your question, both are true: 2TB is the limit if using the PERC 6 (or SAS 6 or S-series controllers), and 3TB is supported on the H-series controllers. The H310 will support larger than 2TB drives, but it is not supported on the R710. It may work, but the H200 was designed to be used in the R710, not the H310, and it will also support >2TB drives with the latest firmware.
Hi,  I need to upgrade disks in my R710. At this moment I have 6x1TB SATA. In the documentation I found that max supported disk size is 2TB. Then I found this <ADMIN NOTE: Broken link has been removed from this post by Dell>  3 TB disk that is compatible with R710. Which information is true as both are from Dell website? I am using H310. Thanks!  
R710 HDD upgrade (max size).