RE: [Xen-users] xen guidelines

[Tom Brown <tbrown@xxxxxxxxxxxxx>]

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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