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[Xen-devel] RE: [Xen-users] Max. PV and HVM Guests

To: <jp.pozzi@xxxxxxxxx>, "Mr. Teo En Ming \(Zhang Enming\)" <space.time.universe@xxxxxxxxx>
Subject: [Xen-devel] RE: [Xen-users] Max. PV and HVM Guests
From: "Robert Dunkley" <Robert@xxxxxxxxx>
Date: Mon, 9 Nov 2009 08:17:31 -0000
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Thread-topic: [Xen-users] Max. PV and HVM Guests
There seems to also be a limit imposed by CPU context switching. Ie. Once you 
have enough VMs trying to grab a cpu core things come to a standstill as the 
cpu spends most of its time switching rather than processing. The most common 
bottleneck I find is disk performance but this depends hugely on what your VMs 
are doing.

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Moi meme
Sent: 08 November 2009 13:02
To: Mr. Teo En Ming (Zhang Enming)
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Max. PV and HVM Guests


The maximum is a direct function of the available memory, every new
machine "eats" some memory and when there is no more memory ......
I had some servers (64bits, 2 quad core and 32Gb Ram) running 19 VM,
2003 server, 2000 Server,Fedora, Debian all in 32bits.
In my own system I have tested with upto 10 VMs of 512M each without
breaking the system.


JP Pozzi

Le dimanche 08 novembre 2009 à 19:45 +0800, Mr. Teo En Ming (Zhang
Enming) a écrit :
> Hi,
> I have observed that there is a maximum limit to the number of PV or
> HVM virtual machines you can start before dom0 hangs or crashes.
> For Fedora 11 Linux x86-64 PV guests, dom0 will crash when I start the
> 7th instance. Max I can start is 6 without crashing.
> For CentOS 5.2 Linux x86-64 HVM guests, dom0 will crash when I start
> the 4th instance. Max I can start is 3 without crashing.
> I have 6 GB of DDR2-800 with Intel Pentium Dual Core E6300 2.8 GHz on
> Intel DQ45CB motherboard.
> Are the above limits reasonable considering the hardware
> specifications of my computer?
> I am using Xen 3.5-unstable changeset 20143 with pv-ops dom0 kernels
> 2.6.30-rc3, 2.6.31-rc6,,, and My host
> operating system is Fedora 11 Linux x86-64.
> -- 
> Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical
> Engineering)
> Alma Maters:
> (1) Singapore Polytechnic
> (2) National University of Singapore
> My Primary Blog: http://teo-en-ming-aka-zhang-enming.blogspot.com
> My Secondary Blog: http://enmingteo.wordpress.com
> My Youtube videos: http://www.youtube.com/user/enmingteo
> Email: space.time.universe@xxxxxxxxx
> Mobile Phone (Starhub Prepaid): +65-8369-2618
> Street: Bedok Reservoir Road
> Country: Singapore
> _______________________________________________
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> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users

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