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Re: [Xen-users] How many guests

To: Michael Schmidt <michael.schmidt@xxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] How many guests
From: Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
Date: Sun, 06 Jun 2010 20:38:54 +0100
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Thanks Micael,

I understand what you are saying.

With a small setup such as a RAID1 array, how many VMs could I rent out?

It doesn't matter if it's a small number, it's just to utilise the server a bit.

Think it would cope with 5-10?


On 06/06/10 20:18, Michael Schmidt wrote:
Hi Jonathan,

if you plan to migrate existing physical machines to xen VMs, or you have some different machines for a comparison, you can easy get runtime statistics and calculate the usage. Look at the running iostats and cpu usage.

If you plan to rent generic VMs on this server to customers, you disk / raid setup will be absolutely the bottleneck. A solution at this point is not easy. If you have much write IOs, use raid 10 with 4 to 8 disks. With many reads - raid 6 or 50 with the same amount of disks.
In each case i can suggest you 15k rpm SAS disks.

Then you can run 29 VMs. Or 60 VMs with 16GB memory and 2 CPUs.

But note: You cannot set disk priority to the VMs. So if one VM does heavy disk IO, all off the other VMs slowed down.

Best Regards

Michael Schmidt

Am 06.06.10 20:45, schrieb Jonathan Tripathy:
Hi Michael,

Thanks for your email.

This is just an idea that I have floating around in my head that maybe I'd like to rent out some VPSs to customers, just to utilise my machine which will be sitting in a co-lo nearly idle.

I'd give out VPSs with 256MB RAM and probably 5Mbps connection speed.

So the answer is, I don't know what will be running on them, however I could write up an "acceptable use policy", as well as use some throttling/scheduling?


On 06/06/10 19:39, Michael Schmidt wrote:
Hi Jonathan,

the question is, what a kind of VM?
You can over-utilize a much greater machine with one VM.
Or on the other side, you can run 40 VMs on a shorter machine.

Each ressource can be a bottleneck

- Memory - this is realy easy to calculate: Avaiable minus 768MB (Reserved for Dom0 should be enugh in this case).
- CPU - Here we need a VM statistic
- Disk Bandwidth - Here we need a VM statistic, but in the most cases not the bottleneck - Disk IOPS - Here we need a VM statistic, in the most cases the botelneck

What a kind of VMs you plane to run?
Webservers / mailservers / database-servers ...?

Best Regards

Michael Schmidt

Am 06.06.10 00:54, schrieb Jonathan Tripathy:
Hi Everyone,

I have a Dell R210 server which has a Xeon X3430 Quad Core CPU (2.4Ghz x 4) with 8GB of RAM. I intend to use the H200 controller in a RAID1 setup

How many VMs do you think I'd be able to run on this machine? Is 20 pushing it?

I'd say most (if not all) guests would be in PV mode.


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