In practically every example of ZFS usage that I've seen online (including several questions here), the zpool is named "tank". Why? Is there some sort of significance to the name or is it just that the original documentation used "tank" so that's what everyone else uses, too? If you have more than one zpool on a system, is it common to have one of them named "tank" or is "tank" only a convention for single-pool systems?
I was confused by this at the beginning as well.
Since the ZFS is referring to 'Storage pools', the author created the nickname 'Tank' as in a 'Tank of water' or a 'Fish tank'. It is a bit of a play on words since the English words 'Pool' and 'Tank' both refer to large containers of water. Some people find it confusing at first.
Here is an old example from the Sun Solaris 11 documentation from 2004:
The term is not referring to a 'Tank' like a Battle Tank, or the term 'Tank' in gaming.
If I find time, I can dig up the authoritative source of the person who created that term. I believe the term was coined by Jeff Bonwick, Team Lead for the ZFS team while at Sun.
Regarding tank - at the OpenZFS Developer Summit 2015 it was stated that they were fans of the Matrix, and it referred to the character "Tank". If you look through the documentation, right along side "Tank" are pools named "Dozer". Funny how the nerd shines through.