Fixing Slow NVMe Raid Performance on Epyc

[thexder1]

@OrbitaLinx

Well since disabeling the scheduler dramatically increases performance its is clearly not necessary.. Maybe it is just for using mixed and matched drives? Does this mean that as long as one uses consistent hardware ZFS is degrading the performance of the pool or pools by adding an additional scheduler? Or maybe the scheduler is just bad?

I am not sure. I suspect that it might be meaningful when you have slower drives especially magnetic drives like these file systems were designed for where the drive is slow enough that requests might wait in queue for a noticeable amount of time. Also of note SSDs tend to have their own queuing on the drive which is why you typically get better performance with none or deadline queues. This is probably a factor here as well.