While that is true of heat pump technology in total, I have not seen any heat pump water heaters in the US that work below freezing. One example: my Rheem manual says it will work down to about 42F / 5C. Below that, it uses resistive heating elements.

But I’m sure it’s coming eventually to water heaters.

GlusterFS is (was) really cool, but I would not set up a new instance. It used to have significant support and development from RedHat, but they decided to halt their work on it, and focus on Ceph.

GlusterFS is getting a few slow updates from some alternate developers, but I would only count on that being fixes for current installations.