CentOS - Dec 2009 - CentOS 5.4 x86_64 only detects 32GB RAM while Fedora x86_64 correctly lists 128GB

Hi,

We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The 64
bits version of Fedora 12 lists the correct amount of 128GB, CentOS only finds
32GB (and so does Scientific Linux). I would much prefer to use CentOS (most of
the software we use is specifically designed for CentOS). Does anyone know what
is causing this/how to fix it?

Many Thanks,

Diederick
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what kernel are you running?

On Mon, Dec 7, 2009 at 2:05 PM, Diederick Stoffers <d.stoffers at
gmail.com> wrote:
> Hi,
> We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The
64
> bits version of Fedora 12 lists the correct amount of 128GB, CentOS only
> finds 32GB (and so does Scientific Linux). I would much prefer to use
CentOS
> (most of the software we use is specifically designed for CentOS). Does
> anyone know what is causing this/how to fix it?
> Many Thanks,
> Diederick
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
>


-- 
Kind Regards
Rudi Ahlers
CEO, SoftDux Hosting
Web: http://www.SoftDux.com
Office: 087 805 9573
Cell: 082 554 7532

Hi,
It seems that this links shed light on the question:
http://lists.xensource.com/archives/html/xen-users/2008-08/msg00934.html
http://www.centos.org/docs/5/html/5.1/Virtualization_Guide/ch-virt-hw-support.html

On 12/07/2009 02:05 PM, Diederick Stoffers wrote:
> Hi,
> 
> We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The
> 64 bits version of Fedora 12 lists the correct amount of 128GB, CentOS
> only finds 32GB (and so does Scientific Linux). I would much prefer to
> use CentOS (most of the software we use is specifically designed for
> CentOS). Does anyone know what is causing this/how to fix it?
> 
> Many Thanks,
> 
> Diederick
> 
> 
> 
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos

Diederick Stoffers wrote:
> Hi,
> 
> We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The 
> 64 bits version of Fedora 12 lists the correct amount of 128GB, CentOS 
> only finds 32GB (and so does Scientific Linux). I would much prefer to 
> use CentOS (most of the software we use is specifically designed for 
> CentOS). Does anyone know what is causing this/how to fix it?
> 
> Many Thanks,
> 
> Diederick
> 
Hi

Very strange. I have a Dell Precision T7500 with 48GB of memory and 
CentOS-5.4 finds everything:
kalyke (Linux)$ uname -rm; free
2.6.18-164.6.1.el5 x86_64
              total       used       free     shared    buffers     cached
Mem:      49453972   48273592    1180380          0     219116   41775056
-/+ buffers/cache:    6279420   43174552
Swap:     50331604          0   50331604
kalyke (Linux)$

Regards

mg.

On Monday 07 December 2009, Diederick Stoffers wrote:
> Hi,
>
> We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The
64
> bits version of Fedora 12 lists the correct amount of 128GB, CentOS only
> finds 32GB (and so does Scientific Linux).
Hmm.. maybe this has to do with the Xen kernel. Redhat says x86_64 should do 
256G/1T (AMD/Intel) and we're successfully running 72G on Centos-5.4.

/Peter
> I would much prefer to use 
> CentOS (most of the software we use is specifically designed for CentOS).
> Does anyone know what is causing this/how to fix it?
>
> Many Thanks,
>
> Diederick
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On Mon, Dec 07, 2009 at 01:05:04PM +0100, Diederick Stoffers
wrote:
>    Hi,
>    We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM.
The 64
>    bits version of Fedora 12 lists the correct amount of 128GB, CentOS only
>    finds 32GB (and so does Scientific Linux). I would much prefer to use
>    CentOS (most of the software we use is specifically designed for
CentOS).
>    Does anyone know what is causing this/how to fix it?
Have you checked "xm info" to see the Xen hypervisor memory info?
Maybe it's just the dom0 linux kernel that doesn't have more than 32G,
and the Xen hypervisor sees all of it.

Anyways, you should always limit dom0 memory to 512 MB or 1 GB to disable
Xen memory ballooning.

If you boot dom0 with all the (32G of) memory visible to it, and then
create VMs, and thus balloon dom0 down to much smaller amount of memory,
you'll get all kinds of problems when the dom0 linux memory suddenly is
much smaller than it was during boot time.

You should always limit and dedicate some amount of memory to dom0.
Use dom0_mem=1G option for xen.gz in grub.conf.

-- Pasi