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RE: [Xen-users] MSSQL and Xen performance

To: "'Fajar A. Nugraha'" <fajar@xxxxxxxxx>, "'Chris Black'" <chrisb@xxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] MSSQL and Xen performance
From: "Dustin Henning" <Dustin.Henning@xxxxxxxxxxx>
Date: Fri, 8 May 2009 09:54:15 -0400
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Another important note regarding using Windows on Xen:
I am pretty sure that using multiple CPUs causes severe performance loss
with the GPLPV drivers provided by James Harper (to the extent that having
one VCPU with the drivers may net better performance than having multiple).
However, I believe the GPLPV drivers still provide better performance with
multiple vcpus than not having the drivers would.  This information could be
slightly dated, but I believe it was recently mentioned by someone else on
the list.  Regardless, some testing of your scenario options would be duly

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Fajar A. Nugraha
Sent: Thursday, May 07, 2009 21:49
To: Chris Black
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] MSSQL and Xen performance

On Fri, May 8, 2009 at 4:30 AM, Chris Black <chrisb@xxxxxxxxxxxxxxxxxx>
> Hello,
> I am working on a xen platform and need to create an MSSQL server. My
> consultant who is doing the installation and setup is refusing to install
> XEN because he says it will cause to much lag and performance issues with
> the system.

At this point I would ask "how much trust you put in your consultant"? :P

As Nathan pointed out, performance would depend on lots of things. In
short, a virtualized environment would impose some performance
penalty. How much the penalty is, depends on your setup. For Linux PV
guests with LVM-backed device, the penalty is very litlle.

For Windows HVM guests, the penalty could be HUGE. That's because you
get penalty from both CPU and disk/network I/O. To increase
performance you can use PV Drivers (like James Harper's GPLPV) which
would reduce I/O performance penalty.

Note that the same thing generally applies to other virtualization
technology as well (Vmware, virtualbox, etc). You need specialized
driver (or "guest additions") to reduce I/O performance penalty.

> Has anyone done an MSSQL+Xen install before and have you experienced any
> major performance problems? Would the community at large recommend a setup
> like this?

I have several Windows 2003 HVM + GPLPV, LVM-backed storage, with
MSSQL Express. They're lightly-loaded though.



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