Re: [Qemu-discuss] Disk Performance

[Dale R. Worley]

> From: Quentin Hartman <address@hidden>

> When running on a ceph-backed volume, I get closer to 15MB/s using the same
> tests, and have as much as 50% iowait. Typical operations that take seconds
> on bare metal take tens of seconds, or minutes in a VM. This problem
> actually drove me to look at things with strace, and I'm finding streams of
> FSYNC and PSELECT6 timeouts while the processes are running. More direct
> tests of ceph performance are able to saturate the nic, pushing about
> 90MB/s. I have ganglia installed on the host machines, and when I am
> running tests from within a vm ,the network throughput seems to be getting
> artificially capped. Rather than the more "spiky" graph produced by the
> direct ceph tests, I get a perfectly flat horizontal line at 10 or 20MB/s.

Is there some sort of virtio for networking?  It sounds like the
guest's driver thinks you've got a low-speed networking card.  I don't
see any options in the qemu command to control your networking
configuration.

Dale