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Re: [Xen-users] redhat native vs. redhat on XCP

To: Javier Guerra Giraldez <javier@xxxxxxxxxxx>
Subject: Re: [Xen-users] redhat native vs. redhat on XCP
From: Grant McWilliams <grantmasterflash@xxxxxxxxx>
Date: Sun, 16 Jan 2011 15:30:51 -0800
Cc: Boris Quiroz <bquiroz.work@xxxxxxxxx>, Henrik Andersson <henrik.j.andersson@xxxxxxxxx>, xenList <xen-users@xxxxxxxxxxxxxxxxxxx>
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On Sun, Jan 16, 2011 at 7:22 AM, Javier Guerra Giraldez <javier@xxxxxxxxxxx> wrote:
On Sun, Jan 16, 2011 at 1:39 AM, Grant McWilliams
<grantmasterflash@xxxxxxxxx> wrote:
> As long as I use an LVM volume I get very very near real performance ie.
> mysqlbench comes in at about 99% of native.

without any real load on other DomUs, i guess
in my settings the biggest 'con' of virtualizing some loads is the
sharing of resources, not the hypervisor overhead.  Since it's easier
(and cheaper) to get hardware oversized on CPU and RAM than on IO
speed (specially on IOPS), that means that i have some database
servers that I can't virtualize on the near term.

But that is the same as just putting more than one service on one box. I believe he was wondering what the overhead was to virtualizing as apposed to bare metal. Anytime you have more than one process running on a box you have to think about the resources they use and how they'll interact with each other. This has nothing to do with virtualizing itself unless the hypervisor has a bad scheduler. 

Of course, most of this would be solved by dedicating spindles instead
of LVs to VMs;  maybe when (if?) i get most boxes with lots of 2.5"
bays, instead of the current 3.5" ones.  Not using LVM is a real
drawback, but it still seems to be better than dedicating whole boxes.


I've moved all my VMs to running on LVs on SSDs for this purpose. The overhead of LV over just bare drives is very very little unless you're doing a lot of snapshots.

Grant McWilliams

Some people, when confronted with a problem, think "I know, I'll use Windows."
Now they have two problems.

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