Recently I replaced the optical drive to SSD to make a fusion drive in my Macbook Pro 13 inch 2012. The hardware installation was successful and it is recognized in Disk Utility. I made a Sierra bootable drive on my 8GB USB drive with DiskMaker X.
The problem is I can't see the USB drive in the boot manager (press option when power up). I'm sure that the USB port in my mac is working. I can see my Time Machine drive in the boot manager and my USB drive after the boot from the original HDD with sierra. I can't make a fusion drive when I can't boot from USB. What can I do?