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> > Is there a guideline for memory? dom0 not less than ??, dom1...domn < ??
>
> It depen of you differents VM and the memory avalaible

Dom0 needs to be large enough to run the various tools effectively. There
also needs to be enough memory to accommodate various driver usages (such as
LVM snapshot metadata etc.).

For starters, try 64 meg and see how well it behaves. You might get away with
less but YMMV.

For the other domains, you need to allocate them enough memory to efficiently
run your services. Ideally, give them about the same memory you would give a
dedicated machine for this task.

> > vm5 - desktop
>
> forget it!

:-)

You can only really do desktop stuff in dom0, since that's the only one
that'll be able to drive the graphics card, sound card, etc. It'd be nice to
split this out more - it may happen in the future.

Running desktop apps isn't an unreasonable config to use for some deployments
(although for maximum security, you'd avoid this). *however* you must bear
in mind that applications in dom0 are one step closer to compromising other
VMs. Therefore, anything you run in dom0 is implicitly more "trusted" the
software in other VMs.

HTH,
Mark

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> When creating a xen server, does it make sense to run any other process on
> dom0, like dns, firewall, dhcp, apache, etc.? I would assume you would
> want as little as possible for performance.
No, for security reason; you should run only ssh (it's really enough)!


> Is there a guideline for memory? dom0 not less than ??, dom1...domn < ??
It depen of you differents VM and the memory avalaible


> If it helps to answer these question with an example config, here you go.
> Setup Xen server:
> vm1 - web server
I will advice, on reverve-proxy mode for Apache then you can have
different VM with specials packages for a groupware system or an ERP.

> vm2 - database server
256 Mb minimum

> vm3 - samba server
256 Mb minimum

> vm4 - network server - firewall, dns, dhcp
64 Mb enough

> vm5 - desktop
forget it!

> vm6 - windows server - future release
256 Mb minimum

For a server, I advice 1 Gb minimum per CPU.
For Virtualization, 4 Gb per CPU.

good luck,
Antoine N.



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> > > Is there a guideline for memory? dom0 not less than ??,
> dom1...domn < ??

And I would like to add: Is there a recommendation for /tmp capacity and
swap size for dom0 ?

I am about to setup a production server and I am eager to hear the
list's experiences with regards to how many resources dom0 needs for
running well.

I guess that there is no great need for driver memory in case a domU is
running off physical partitions since the disk access then goes directly
through the hypervisor (?). But what about when dom0 is serving
file-backed vbd's ? Will a 64 MB dom0 behave like a normal file server
with only 64 MB mem ?

Cheers
-- Jan Holst Jensen, Novo Nordisk A/S, Denmark

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I would like to ask a variant of the original question. Will extra memory
allocated to dom0 effectively become disk cache for all the domU's ?

I have also included my replies to Jan's questions in context below.

-Tom

On Mon, 11 Apr 2005, JHJE (Jan Holst Jensen) wrote:

> > > > Is there a guideline for memory? dom0 not less than ??,
> > dom1...domn < ??
>
> And I would like to add: Is there a recommendation for /tmp capacity and
> swap size for dom0 ?
>
> I am about to setup a production server

AFAIK, that is like asking what type of vehicle you should buy for work.
(Without specifying what kind of work you do :-)

Database servers, mail servers, webservers, compute nodes, etc have far
different usage patterns. Whether any of those services are in dom0 or
domU may be significant.

In my very limited experience, /tmp is irrelevent as xend won't need it,
but then I haven't used the migrate or save commands. AFAIK dom0 doesn't
need much memory and shouldn't be doing much work, so it shouldn't need
(much?) swap. I haven't configured swap on the one box I have running, but
then it isn't 100% stable either :(

> and I am eager to hear the list's experiences with regards to how many
> resources dom0 needs for running well.
>
> I guess that there is no great need for driver memory in case a domU is
> running off physical partitions since the disk access then goes directly
> through the hypervisor (?). But what about when dom0 is serving

No. It still goes through the dom0 kernel to get to the hard drives, as
the hypervisor doesn't know much about the hardware (with apologies to the
programmers, not much in comparison to the Linux kernel that has all the
device drivers :-)

> file-backed vbd's ? Will a 64 MB dom0 behave like a normal file server
> with only 64 MB mem ?
>
> Cheers
> -- Jan Holst Jensen, Novo Nordisk A/S, Denmark
>
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>

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> I would like to ask a variant of the original question. Will
> extra memory
> allocated to dom0 effectively become disk cache for all the domU's ?

Thanks Tom. That is precisely what I was trying to ask.

> AFAIK, that is like asking what type of vehicle you should
> buy for work.
> (Without specifying what kind of work you do :-)
>
> Database servers, mail servers, webservers, compute nodes,
> etc have far
> different usage patterns. Whether any of those services are in dom0 or
> domU may be significant.

I would setup the server so that dom0 does nothing but provide I/O
services and control the domU's. I am used to running GSX so I am
thinking along the lines dom0="host OS" and domU="guest OS".

> > I guess that there is no great need for driver memory in
> case a domU is
> > running off physical partitions since the disk access then
> goes directly
> > through the hypervisor (?). But what about when dom0 is serving
>
> No. It still goes through the dom0 kernel to get to the hard
> drives, as

Ah yes. Of course. Thanks for clearing that up.

Cheers
-- Jan

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