[ale] Question about Virtual Nics and Speed

[David Tomaschik]

On Wed, Jun 5, 2013 at 11:29 AM, Chuck Payne <terrorpup at gmail.com> wrote:
> Guys,
>
> I am currently running a couple Kernel Virtual Machines (KVM) servers,
> today my db admin told me that he noticed that the speed isn't great
> on a rsync he was doing. I looked and notice that he was only transfer
> about 300MB per second. So I started digging into why is that,
> everything should be at about 1Gig in speed.
>
> I told a look network devices on the server with ip
>
> ip link show
<snip>

ip link show doesn't expose the connection speed of your interface, so
I'm not sure what leads you to believe your vnic is at 500Mb/s.  If
you're talking about the "qlen 500", that's the txqueuelen, or the
number of packets that the kernel will queue for that interface at any
given time.

> I am using e1000 as my virtual nics
>
> -device e1000

If your guests have a relatively recent kernel, you should be able to
use virtio-net as your driver instead of e1000.  It has significantly
lower overhead, so if your guests are starving the host CPU, this can
help some.

>
> Is there a setting I need to check?  Is it control by brctl? Or 500MB
> the best I will get.

As others have pointed out, 300MB/s is actually not possible over a
1gig link.  You might be getting 300MB after compression, which would
be great, or 300Mb, which is not ideal, but also possible.

In all likelihood, your bottleneck is at rotating media somewhere,
unless you have a fast SAN or RAID array.


--
David Tomaschik
OpenPGP: 0x5DEA789B
http://systemoverlord.com
david at systemoverlord.com