1. Reformat both the drives (if necessary)*
2. Mark both drives as  boot device

2. Resize EFI boot partition from default 1GB to 250MB for both drives

 3.Add an GPT partition to both the drives (assign same size and unformated )

4. Create a software RAID and select the partition that you created 

5. Create a Logical Volume Group

6. Create Logical volumes –  Ex: (for 250GB-2-SSD)

• Root – 30GB
• Swap — 4GB
• Var — 20GB
• Home — 140GB

Press Done

7. Provide your Username and Password 

8. Make sure press finish to  after the installation log shows success