The default setting on the server is to use a BIOS... any computer using a bios can only boot to an MBR disk. MBR disks are capped at 2048GB (=2TB). Data drives become a whole different story. From the factory I don't believe they offer the option to slice the raid set (though it is an option in the PERC bios). With UEFI enabled (and an OS that supports this (Windows 2008 x64, 2008 R2, 2012, VMware ESXi 5.x, most modern linux distros)) you have to boot to a GPT disk, which can be larger than 2TB. The online configuration website doesn't have the option to pick UEFI, so online it probably won't let you pick a (boot) raid set larger than 2TB. If it offers a raid option that makes the first raid set smaller than 2TB, you can then always recarve the raid when you receive the unit and enable UEFI if needed/desired.
PE710 - RAID10 larger than 3.6TB total capacity?