Re: But what does it do?
Given a load of servers running Kubernetes (a container orchestrator) that have locally-attached storage, it uses said local storage to create a set of network block storage devices (accessible via eg. iSCSI).
There's nothing particularly magic in the approach as far as I can see, and there's a few open source options that can do such (eg. Ceph) as well as your enterprise-friendly $$$ storage vendors. The former (and a lot of the latter) have some quite interesting corner cases in terms of operability, so if they can file off a few of those it might be worth a peek.
As with all things storage / database wise, such things are best watched from a distance until the sharp edges have cut someone else first.