Hello,
Do not confuse Dom0 with the hypervisor... The hypervisor in
RHEL5 is able to use 256 GB of memory. You can (and I would recommend
you do so) limit the initial memory size for Dom0 using the parameter
dom0_mem in grub.conf. E.g. kernel /xen.gz-2.6.18-92.1.6.el5
dom0_mem=524288 for 512 MB Dom0.
I can say that Xen works fine on 64 GB and with up to 24 GB
DomUs.
Regards,
Daniel
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Tom Georgoulias
Sent: Thursday, July 17, 2008 6:40 PM
To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list
Subject: Re: [rhelv5-list] memory limitations for dom0 kernels in 5.2?
Stephen John Smoogen wrote:
> On Thu, Jul 17, 2008 at 8:14 AM, Tom Georgoulias
> <[EMAIL PROTECTED]> wrote:
>> Trying to get some clarification on RAM limitations in for
>> virtualization in
>> 5.2 because I'm not finding the info I need in the knowledge base or
>> the latest 5.2 virtualization manual.
>>
>> In 5.1, a 32bit dom0 couldn't use more that 16GB of RAM. In
>> addition, a special boot option needed to be used to get a 64bit dom0
>> to use more than 32GB. I got that info from here:
>>
>> https://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/en-US/RH
>> EL510/Virtualization_Guide/ch-virt-hw-support.html
>>
>> One of our older 32bit HP servers that is running xen was restricted
>> from using half of its RAM because of the 16GB limitation mentioned
>> above and I'd like to avoid any surprises with our new hardware
>> purchase. We will be getting a new x86_64 based server to run a
>> rhel5.2 64bit dom0 and a mix of
>> 32 and 64 bit guests, and this server will have 32-64GB of RAM
>> (depending on the cost, of course!). I've looked through the
>> virtualization manual for
>> 5.2 and couldn't find any mention of the RAM limitations that were
>> spelled out in the 5.1 manual, so I was wondering if anyone had some
>> advice. My gut says we'd be OK with 64GB but I'd like some
clarification if possible.
>>
>
> As far as I know, the 16 GB is still a limit for 32bit dom0's, I think
> processes are limited to 3.2->4 GB in size. I do not know about 64 bit
> ones. To be honest.. if you have something needing that much memory..
> is it a good candidate for virtualization?
Oh, our domUs will be 32/64 bit and between 512m-4GB in size, nothing
larger. Dom0 will be 64 bit and will likely pretty small (memory wise)
once we get all the VMs running. I just wanted to be sure that if we
bought a server with lots of RAM, we would be able to use all of it.
Tom
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