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MDADM RAID Caching?

How do I go about SSD caching a MDADM RAID array with SSDs?

I setup Ubuntu 18.04.3 Server on an SSD. Then I made a RAID 6 array with MDADM. I have 2 spare NVMe 970 EVO drives I want to use to cache the RAID. I have not found a solid answer on how to do this.

I have tried ZFS in the past on Ubuntu 18.04 server but had an issue where upon reboot, the ZPool would not be added unless I manually added the pool which as you can imagine is not particularly wanted in a production environment.

I currently have the 2 NVMe drives also setup in MDADM as a RAID1 array to simulate a ZFS Cache pool but dont know where to go from there.

Should I make an LVM2 Volume Group of the RAID 6 array and the another Volume Group for the Cache pool? Then setup lvmcache between the 2?
Not sure how to do that exactly.

For lvmcache… The drives have to be in the same VG.