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Re: Slow read(2) and write(2) syscalls

On Wed, 29 Apr 2020 15:55:31 +0100
Mike Pumford <> wrote:

> I haven't tried with anything later than 7 but I use virtual box
> hosted on windows a lot with ahci storage emulation. In the last
> tests I did I was getting 100MB/s write performance with both Ubuntu
> (kernel 4.4) and NetBSD 7.  For reference the underlying disk in that
> case was a 2TB ATA attached to an AHCI controller.

What I notice when writing data to disk, with Linux VM there is very
little CPU usage on the physical host, but with NetBSD (and other BSDs
I guess) CPU usage shoots up. So Linux definitely has some
optimizations. Not sure if this is down to Oracle guest additions, or
Linux KVM acceleration. Or maybe it's NetBSD FFS, I got much better
throughput with NetBSD + ZFS but that used 4 striped virtual disks.

Tests below used 1 MiB block size, writing non-compressible data to the
same 2TB SATA disk.

Linux physical host running VirtualBox:
Total 5.00 GiB: 36832.69 msec, 139.01 MiBs, 139.01 Ops

Linux VM with XFS:
Total 5.00 GiB: 60461.32 msec, 84.68 MiBs, 84.68 Ops

NetBSD-9 VM FFS with logging:
Total 5.00 GiB: 138410.84 msec, 36.99 MiBs, 36.99 Ops

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