This is quite clever. I had tried a simpler version of this a few years back on AWS using LVM cache[1], attached SSD disks (for the cache) and EBS volumes (for the persistent storage). For our workloads (big data processing with Hadoop/Hive), the performance benefit was not significant, so we dropped it.

1. https://access.redhat.com/documentation/en-us/red_hat_enterp...