Re: [Xen-users] RHEL 5.2 i386 image - Xen kernel doesn't recognize the total amount of system memory

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Jul 29, 2008 at 06:06:40AM -0500, aaron@xxxxxxxxxxxx wrote:
> Hi Ido,
> 
> We recently made multiple attempts to get Xen 32bit kernel (centos OS)  
> using 32GB, and all were unsuccessful. The OS would only allow use of  
> the first 16GB.  We have since tested the same hardware on 64bit, and  
> you can utilize all 32GB without any issues!
> 

With RHEL 5.2 (and CentOS 5.2) you should be able to run 64b hypervisor with
32b domU's.. so you could have 64b hypervisor (seeing all the memory) and
split it between multiple 32b domU's (and 32b dom0, if you want).

Or then run 64b hypervisor + 64b dom0 + 32b domU's.

-- Pasi

> Regards,
> Aaron
> 
> 
> Quoting Ido Levy <IDOL@xxxxxxxxxx>:
> 
> >Tom,
> >
> >Thanks for the info.
> >
> >Do you know if RHEL 4.5/6 32 bit image Xen kernel supports more than 16GB
> >of RAM ?
> >
> >Ido Levy
> >
> >
> >
> >
> >             Tom Georgoulias
> >             <tomg@mcclatchyin
> >             teractive.com>                                             To
> >                                       Ido Levy/Haifa/IBM@IBMIL
> >             28/07/2008 23:45                                           cc
> >                                       xen-users@xxxxxxxxxxxxxxxxxxx,
> >                                       Alexandra Kisin/Haifa/IBM@IBMIL
> >                                                                   Subject
> >                                       Re: [Xen-users] RHEL 5.2 i386 image
> >                                       - Xen kernel doesn't recognize the
> >                                       total amount of system memory
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >Ido Levy wrote:
> >
> >>We have installed RHEL 5.2 Server ( i386 image ) on a machine with 64GB
> >of
> >>RAM.
> >>
> >>When booting the default PAE kernel ( 2.6.18-92.el5PAE ) that is shipped
> >>with RHEL 5.2 installation the OS detects 64GB of RAM.
> >>But when booting the Xen kernel ( 2.6.18-92.el5xen ) the OS detects only
> >>14GB of the total amount of available RAM.
> >>
> >>Did anyone encounter this problem before ?
> >
> >I did when I first installed RHEL5.1 on a server with 32GB of RAM.
> >
> >>Is it a normal behavior for a 32 bit image ?
> >
> >Yes, 32-bit supports up to 16GB.  To use the rest of the RAM, you'd need
> >to install the 64-bit kernel-xen.  Some docs are here:
> >
> >https://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/en-US/RHEL510/Virtualization_Guide/ch-virt-hw-support.html
> >
> >
> >Hope that helps.
> >
> >Tom
> >
> >
> >

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