Can I have 4 disks of 4 TB each and I have two raid 1 of 4 tb so I have 8 TB of space?
Yes, you can run “Dual Mirror” on the EX4100.
https://support.wdc.com/knowledgebase/answer.aspx?ID=12965#4-bay
You would choose RAID 1 and then choose the two drives to use and then setup volume 1, repeat the process for the other two drives as volume 2. When you create shares, you need to choose which volume the shares will be created on. Try to not use the same names for shares on both volumes to avoid confusion when browsing over the network.
