Rudolf Meier

That was also my finding when I tried to combine SSDs with my HDD-RAID. I also tried to accelerate a raid with an LSI controller and cache cade... but guess what? They don't support NVMe because "it is faster than hdds" ... that's really what they sayed ? ... so the only option was to combine a "normal" SSD (so, those that have a transfer rate of about 500-700 MB/s) with my HDD-RAID (with a transfer rate of 600-800 MB/s) ... and... sure, lower latency, but I didn't think that's useful. That's why I switched over to Intel CAS... it seems to work pretty well, even with slow SSDs (at least in the tests I made... I'm waiting for some cables but when I get them I will use it in our new servers with NVMe disks). One interesting thing here is, that it also uses RAM as reading-cache. The only problem I can imagine to run into is that my SSDs could be too small. But, we will see... I'm trying it with 1 TB of SSD space per 12 TB of (usable) HDD space.

That wasn't a joke... I'm serious about this... try Intel CAS... I think that's providing what you want... or at least it would be worth a try and maybe you can create another video from this experiment... and it's not that expensive (even free if you use Intel ssds) And by the way, it also answers another question you had on a board... "who is ever using 4 U.2 drives in one system??" ... well, the guy that's using those ssds as a cache

Why didn't you try the "Intel Cache Acceleration Software" ?? It's free if you use it together with Intel SSDs and my finding was, that this is the best SSD caching solution (I tried many, including those integrated in raid controllers). No idea if it's an option for you, but it might be. In theory you should be able to combine a drive (or raid of whatever kind) with either an ssd or for example a raid-0 of ssds. I'm using it with "ordinary" U.2 ssds of Intel to accelerate our Hyper-V servers.