I'm running 2 different brand 2TB drives in a RAID1 configuration. I had difficutly setting up RAID1 - i.e. it formated both drives. But seems to be running well.
Here are the model numbers from a disk test from the DNS.
Manufacturer: Seagate
Model: ST32000542AS
Size: 2000 GB
Manufacturer: Hitachi
Model: HDS722020ALA330
Size: 2000 GB