This platform comes with an Active SAS BackPlane – ASR1500SASBP Kit.
It can supports upto 3 hot-swap 3.5” SAS/SATA Drives.
From the tested hard drive lists:
There are hdds like the Hitachi, Deskstar 7K1000.GB HDT721010SLA360 - 1TB, which means that up to 3 TB should be okay.
I guess that the chipset is capable of supporting much higher storage capacity than this. But for your platform, i guess that 3 TB would be the maximum.
All the best,