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RE: [Xen-users] Resource allocation for two VMs

To: "Richard Ginzburg" <richard@xxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Resource allocation for two VMs
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Thu, 10 May 2007 15:43:29 +0200
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Thread-topic: [Xen-users] Resource allocation for two VMs
> -----Original Message-----
> From: nassegris@xxxxxxxxx [mailto:nassegris@xxxxxxxxx] On 
> Behalf Of Richard Ginzburg
> Sent: 10 May 2007 14:34
> To: Petersson, Mats
> Subject: Re: [Xen-users] Resource allocation for two VMs
> Thanks for your reply! Well, let's say I want the two VMs to 
> use the equal, maximum amount of
> system resources and only leave enough for the physical machine to be
> able to run Xen and not choke? 

Well, if you run two domains of equal type (two databases, two
firewalls, or two generic Linux distributions for software compatibility
testing, for example), then I'd assign "sufficient" memory to Dom0 (this
will depend on the load that the guests put on Dom0, so it's not trivial
to say, but something like 256MB should be a good starting point - you
may need to increase or decrease it depending on statistics in Dom0
(top, iostat, memstat or such). 

Then split the remaining memory (e.g. 2.75GB -> 1375MB each) to the two
domains. [You may have to check the "free memory" in "xm info" to see
exact amount of available memory, as Xen itself will use a little bit of

> On 5/10/07, Petersson, Mats <Mats.Petersson@xxxxxxx> wrote:
>       > -----Original Message-----
>       > From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
>       > [mailto: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> <mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx> ] On Behalf Of
>       > Richard Ginzburg
>       > Sent: 10 May 2007 13:10
>       > To: xen-users@xxxxxxxxxxxxxxxxxxx
>       > Subject: [Xen-users] Resource allocation for two VMs 
>       >
>       > Hello!
>       >
>       > I'm setting up two Xen virtual machines on my server (spec
>       > below). Whats the maximum
>       > amount of ram and disk I should allocate for the VMs for good
>       > performance? The server will not run anything else.. 
>       This is like asking how big a van/truck/lorry I need to move the
>       contents of my house, without giving any indication of 
> how large my
>       house is, or whether it is choked with furniture or 
> only sparsely
>       furnished. 
>       The real answer is "the same amount of memory you would use in a
>       'physical' machine". So if you have a medium-sized 
> database server, you
>       may need 1-2GB. A firewall will probably do fine with 128MB. 
>       Diskspace is the same story - figure out what disk-size 
> you'd use for a
>       "real" server, and then allocate that much space from 
> your disk -
>       firewall would be a gigabyte or two (enough to install 
> the OS and not 
>       much more), database server would be the size of the 
> database + OS
>       install + extra.
>       --
>       Mats
> -- 
> Regards,
> Richard 

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