Hello I have created a raid6 array with 6 physical drives (all same size). I would like to add a cache drive to it. I did a google search and the AI is talking about being able to use the mdadm --write-journal option to specify a ssd for write journaling, which apparently uses the SSD to cache writes. It doesn’t mention anything about reads.
Other searches suggest using dm-cache.
I’ve setup the array, and am testing and playing but I have some time to try things out. I’d ultimately like to end up with some kind of NVMe caching option. In a perfect world I’d like to be able to use a NVMe RAID1 array (mirror) in case one of the NVMe craps out on me.
Does anyone have experience with something like this? Can you offer me something better than random google AI stuff that keeps coming up? Given the initial build time of the array was several days I’d love to get it right this next time 
Thanks!
As I understand it ZFS is not officially supported in Tumbleweed. There are ways to get it, but I’ve heard that kernel updates will occasionally break it. I need the file system to be stable. Are you suggesting ZFS is solid in Tumbleweed?
@JBinFla It’s out of tree, so not supported, it does break at times…
This is software raid made with mdadm. I found a bit online on the SLES 15 documentation but it’s all a bit “techno” for me. I am hoping for an idiots understanding of using bcache for this. It does seem that bcache is “on top” of the underlying filesystem which is nice I think as long as it’s clean you can enable / disable it? I’m not sure I’ve found a lot of technical documentation but it’s mostly over my head, I’m just trying to find the “for dummies” version.
Create md devices the normal way and pass those to Stratis, it takes care of encryption, caching, filesystem, and scaling. 
https://stratis-storage.github.io/
They’re working on adding raid support in the future, i.e., it won’t manage mdraid for you just yet. 
This topic has nothing to do with hardware, mdadm is pure software solution. It should be moved to Applications.
Then you need to explain what you are trying to achieve. “cache drive” is highly ambiguous and can be understood rather differently.
abandoning this post, making a new one in Application.