Re: NetBSD block vs raw disk I/O

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

On Sat, 11 Aug 2018 18:09:15 +0200
Martin Husemann <martin%duskware.de@localhost> wrote:

> On Sat, Aug 11, 2018 at 04:02:44PM +0100, Sad Clouds wrote:
> > Hi, so you're saying that with ucb_direct read/write on mounted file
> > system should also speed things up compared to NetBSD-8? I see
> > terrible I/O performance with NetBSD running as a VM on a
> > VirtualBox, just reading/writing regular files is quite slow
> > compared to Linux VMs on the same hardware. I've never been able to
> > figure out the reasons for it, maybe Linux has better integration
> > with VirtualBox and better optimisations.
> 
> We had a similar discussion on some list a while back and I did some
> timings. My values were close to the ones others cited for Linux and
> others said their NetBSD timings were a lot worse than mine.
> 
> I use SATA and NVMe emulations in virtual box, and mount all
> filesystems on the emulated SATA drives with "log".
> 
> Don't think I had to tweak anything special on the host or in virtual
> box.
> 
> Martin

Yes we did, however I only get about 50 MB/sec on a NetBSD VM, file
system mounted with "log", while Debian physical host that runs
VirtualBox-5.2.16 is capable of around 800 MB/sec:

$ dd if=/dev/zero of=out bs=1M count=10000 conv=fsync
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB, 9.8 GiB) copied, 13.0382 s, 804 MB/s

Yes there will be some virtualisation overhead, but not this much. I
started comparing raw device I/O on NetBSD VM and got around 200 MB/sec,
but that is still somewhat less than what I was expecting.

But if I boot NetBSD on this physical hardware from a second disk and
read raw device that contains Debian on RAID0 SSDs, I get around 890
MB/sec. So there is something weird about running NetBSD in a
VirtualBox. Linux VMs don't seem to have such issues. There are a few
other things I'm going to try, but at the moment I just don't know what
causes this.