@scottalanmiller Yes. This I know. But this isn't bare metal but rather SmartOS hypervisor in a Triton datacenter. So I presume all is atop ZFS. I never delved deeper so honestly do not know.
Hopefully not, as ZFS isn't all that fast. But you need XFS touching WiredTiger... what's lower in the stack isn't what it is concerned with. You still control your own filesystem regardless of what the datacenter may or may not use elsewhere.