On the other hand, algae do not produce shade, not sure if it filters atmospheric pollutants, and trees provide all sort of other services to the local ecosystem.
Maybe this invention can be used on places where trees cannot lives, but I’d still take a city with trees over a city full of green tanks.
You don’t need 4 drive for redundancy, 2 is enough. You only need 4 minimum for a raidz2, or raid 10.
My setup uses a pair of SSD in mirror for apps, and a 5 disk raidz2 (4 data disk + a hot spare) as a main data backbone.