Please see my post at
Increasing sharespace capacity from 4*1 TB 4*2 TB
I am resurrecting that thread. Before buying new drives, allow me a day or two to test a few things.
I am in the same situation whereas 2 of the 4 drives have basically crapped out. I have seen these
drives fail in regular desktops as well. They are junk and fail rather quickly in some cases I have seen.
And yes these drives are only 5400 rpm instead of the better 7200.
These drives can however still be purchased