Disk asyncIO in what operating systems is there support?

Question

linux

I study highload at my leisure. Faced with the fact that everyone recommends aio on nginx, but in the same ubunt it is actually disabled. Google didn't help much. The only thing I understood is that you need to install FreeBSD 9 or higher, there is support there. Do I understand correctly that it’s really not possible to squeeze performance with hdd even with aio, is it better to immediately ssd?