Re: [Xen-users] streaming server on a virtual machine.

[Brian Krusic <brian@xxxxxxxxxx>]

Hi Grant,

I'm curious about your tests; LVM vs non LVM for the domU.

Was your domU image based (sparse or no sparse) and using an LVM inside or did you set up your domU to have direct disk access?

Was your dom0 LVM based as well?

What non LVM fs were you using, ext2, ext3, XFS?

- Brian

On Sep 26, 2009, at 7:05 AM, Grant McWilliams wrote:

On Sat, Sep 26, 2009 at 2:42 AM, Mauro <mrsanna1@xxxxxxxxx> wrote:

2009/9/18 Jeff Sturm <jeff.sturm@xxxxxxxxxx>:

> I don't see why not.  If you're concerned about latency you could always
> pin the server to a physical CPU.
>
> (Lately we've been doing a lot of physical-to-virtual migrations, and
> I've found myself asking: "What kinds of servers do we have that should
> never be virtual?"  There aren't many on that list.)
>

You say that a streaming server can be installed on a virtual machine.
I don't want to create any kind of disturb but I've asked the same
question to the KVM mailing list and they said that a streaming server
(I user red5), due to the high I/O traffic, it must absolutely not
virtualized.

That may be true on KVM, I don't know. Databases are usually the most brutal on VMs and I ran mysqlbench (all tests) on
KVM as well as on the same machine native. KVM was within 5% of the native test. I did the same thing
with Xen 3.4.0 and the performance was within 4% but when I moved my database storage to an LVM
LV on DomU used as a hard drive in DomU the difference fell to less than 1%. Yes, the very IO dependent
mysqlbench speed improved substatially when using LVM over disk files. The only real difference between
mysqlbench on the real server and then on Xen/LVM was 20% higher CPU utilization.

I will also add that if Xen has a bottleneck it's traffic between DomUs. Don't configure it in any way to have
one DomU servicing another DomU unless both have real  network cards attached to them. As strange as it
sounds I've clocked 3x speed improvement by sending the data out of the machine to a switch and back in
to another DomU as apposed to sending it straight across. There's something messed up in that but if you follow
this guideline you'll get wire speed out of your DomUs.

My advice, set up the streaming server and watch it. If it doesn't work migrate it to new hardware. What are you out?
The other note I'd add is that if your server is running at 100% utilization there's no benefit in Virtualizing it. You will
only know if it's worth it by doing it and watching.

Grant McWilliams

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