Sodapops, If you create a Virtual Disk with drives that are 2TB and 3TB in size, you will have some space that is not able to be used. It will only use 2TB of the 3TB drives but you will be able to add the drive to the array. I hope this helps. Let me know if you have any other questions.
We have an MD1200 with seven 2TB drives.  We need to expand it.  Dell does not have 2TB drives anymore.  I have a quote for five 3TB drives and the sales rep said they are compatible. This is on a PowerEdge R710 with an H800 card using Server 2008 R2 setup as a GPT volume. Question: Can I make one virtual drive out of physical disks with different sizes?  If yes does that waste space on the largest drives?  We are using this as an archive location (speed doesn't matter), so RAID5 with a hot spare would suffice.  We can delete the array if needed and restore data back to it.  One Virtual Drive would be ideal, but we can split it up into two if necessary. Thanks!
MD1200, PERC H800, one virtual drive, using physical disk with different sizes