[CentOS-virt] Mixed dom0/domU usage?

Wed Feb 4 13:46:11 UTC 2009
Christopher G. Stach II <cgs at ldsys.net>

----- "Dennis J." <dennisml at conversis.de> wrote:

> Hi,
> I'm wondering about the impact of using both dom0 and domU's on a
> server at 
> the same time. I'm worried about the performance impact of running a
> Mysql 
> server in a domU and now I'm thinking about moving the Mysql part of a
> setup into dom0 and running a few Apache guests as domUs. Since the
> Apaches 
> will serve mostly from an NFS share they won't have much impact on the
> disk 
> i/o so the database should be able to utilize the local storage
> without 
> much interference from the guests. The plan is to limit dom0 to let's
> say 
> 4gb of ram and then use the rest of it for the VMs.
> Has anyone experinece with this kind of "mixed" setup
> (physical/virtual). 
> Are there any known problems with this approach?

Running processes in dom0 that aren't for running Xen is going to destroy your domU I/O performance.  The backends are just processes.  If you take time away from those processes for other things, performance will suffer.  You should run some load tests and see if it suits your model, though.

Running the MySQL process in dom0 isn't going to get you very much of a performance boost if your MySQL configuration is tuned properly, either.

Christopher G. Stach II