If your external hard disks are ejecting while in use and you are trying to figure out why, this FAQ at the SoftRAID site may help.
According to SoftRAID’s tech team, it could be a glitch with the version of OS you are running on your Mac. According to the tech experts, “We now know that a problem in the MacOS system software is the cause of disks ejecting while in use. This problem is fixed from MacOS 10.12.2 onwards. We strongly recommend that you upgrade to MacOS 10.12.2 or any later MacOS version if you have encountered this problem.”
The folks at SoftRAID have complete instructions for you on their FAQ page mentioned above. Yes, you can fix this, but only if you check out their road map.