As far as I'm aware ZFS does not scale out.

https://unix.stackexchange.com/a/99218

Yea, it wasn’t designed to scale that way.

In principle you could use fiberchannel to connect a really large number (2²⁴ iirc) of disks to a single server and then create a single ZFS pool using all of them. This lets you scale the _storage_ as high as you want.

But that still limits you to however many requests per second that your single server can handle. You can scale that pretty high too, but probably not by a factor of 2²⁴.