Re: Qemu storage performance drops when smp > 1 (NetBSD 9.3 + Qemu/nvmm + ZVOL)

[B. Atticus Grobe]

ZFS (at least on Solaris and FreeBSD) will use any uncommitted RAM as an
I/O buffer, which likely explains why it was keeping up with the single
core runs, pushing everything to RAM instead of to disk. I would expect
if you push enough data to fill that buffer up, you'll see an equivalent
drop in write speed.