Re: NetBSD block vs raw disk I/O

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

On Sun, 12 Aug 2018 15:52:44 +0100
Sad Clouds <cryintothebluesky%gmail.com@localhost> wrote:

> 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.

OK, I cloned NetBSD VM, kept everything the same, but installed Debian
with XFS file system.

$ dd if=/dev/zero of=out bs=1M count=10000 conv=fsync

this gives 682 MB/sec which is what I would normally expect