Right now i have a RAID 5 Array with 4 3TB Western Digital WD Green WD30EZRX. I've read reviews on HDDs for RAID and i saw that Hitachi ULTRASTAR are one of the best for RAID. I would like to move to the Hitachi HDDs but my server is live and has lots of data on it. So my question is can i swap out my WD HDDs one at time until they've all been replaced? or do i have to take the hit and redo the array from scratch?