RAID recommendations for Mac Pro 5.1 cheese grater

I'd like to get my fcpx libraries onto a RAID. While I don't have Thunderbolt, I do have USB 3 and SATA, and I don't mind paying for a Thunderbolt RAID for future compatibility as long as it also has USB or SATA.
Thanks!

I don't think you can add Thunderbolt to a 5,1 Mac Pro. People add USB 3.0 PCIe cards but there's wide variation in compatibility. I have a few small two-drive Western Digital MyBook USB 3 RAID boxes, and they work on my iMac and iMac Pro. However IMO USB 3 isn't ideal for larger RAID systems.

Supposedly this CalDigit card will provide eSATA, USB-A and USB-C. I have no idea if it works in a 5,1 Mac Pro or what the compatibility issues are: www.caldigit.com/Fasta-6GU3plus/

This really isn't a FCPX issue, it involves Mac hardware, 3rd party interface cards, compatibility/stability, and macOS.

yes Thunderbolt is out of the picture for any pre-2013 Mac Pro.
No PCI card or whatever kind of extension will ever bring it, it has to be implemented to the motherboard from conception.
As for the www.caldigit.com/Fasta-6GU3plus/ joema is mentionning it works great in a 5.1 MacPro (I have one...) High Sierra so far ...

Thanks for the replies. I apologize for the question since you are correct that this is not an fcp topic. I'm trying to figure out how to make the files for my fcp work in progress more robust since TimeMachine appears to be too slow. I'm thinking of moving my libraries to a RAID 5 to at least cover a hard disk failure event. This question should have been focused on experiences with fcpx libraries on RAID.

I posted another question about backup strategies for fcp on this forum so hopefully I'll get a bit of feedback there.