Hypervisor Memory Limitations on 64-bit Architecture?

Hypervisor Memory Limitations on 64-bit Architecture?

[Joshua West]

Hey all,

I'm wondering if anybody could shed some light on this subject.  Are
there limitations as to how much RAM a 64-bit Hypervisor will
recognize/support under the Xen 3.1.x or 3.2.x series (or the upcoming
3.3.x if anything has changed)?

>From what I recall, a 32-bit Xen Hypervisor will recognize up to 16GB of
RAM and a 64-bit Xen Hypervisor will recognize up to 32GB -- but I'm not
certain on if 32GB is in fact the upper limit for 64-bit Xen.

Thanks.

-- 
Joshua West
Systems Engineer
Brandeis University
http://www.brandeis.edu

Re: Hypervisor Memory Limitations on 64-bit Architecture?

[Pasi Kärkkäinen]

On Fri, Jul 18, 2008 at 12:56:34PM -0400, Joshua West wrote:
> Hey all,
> 
> I'm wondering if anybody could shed some light on this subject.  Are
> there limitations as to how much RAM a 64-bit Hypervisor will
> recognize/support under the Xen 3.1.x or 3.2.x series (or the upcoming
> 3.3.x if anything has changed)?
> 
> >From what I recall, a 32-bit Xen Hypervisor will recognize up to 16GB of
> RAM and a 64-bit Xen Hypervisor will recognize up to 32GB -- but I'm not
> certain on if 32GB is in fact the upper limit for 64-bit Xen.
> 

http://www.redhat.com/rhel/compare/

RHEL5 supports 16 GB of mem on x86 (32bit) platform. 
RHEL5 supports 256 GB of mem on x86_64 platform.

And RHEL5 contains Xen.

http://www.nabble.com/Unable-to-start-hvm-guest-on-cs16998-td15419631.html

"Running Xen Unstable changeset 16998 (pulled  20080208) on Unisys ES7000/one 64x 256gb with SLE10SP1 x64."

There you have an actual server with 256 GB of mem running Xen :) 

(yeah, the mail is about problems, but hey, it's xen-unstable repository
they're testing there :)

-- Pasi

Re: Hypervisor Memory Limitations on 64-bit Architecture?

[Joshua West]

Hi Pasi,

Thanks for the information.  Do you have any details regarding x86_64
architecture memory limits with the Xen Hypervisor, using stock Xen --
instead of those modified/patched by vendors like Red Hat?

Thanks.

Pasi Kärkkäinen wrote:
> On Fri, Jul 18, 2008 at 12:56:34PM -0400, Joshua West wrote:
>   
>> Hey all,
>>
>> I'm wondering if anybody could shed some light on this subject.  Are
>> there limitations as to how much RAM a 64-bit Hypervisor will
>> recognize/support under the Xen 3.1.x or 3.2.x series (or the upcoming
>> 3.3.x if anything has changed)?
>>
>> >From what I recall, a 32-bit Xen Hypervisor will recognize up to 16GB of
>> RAM and a 64-bit Xen Hypervisor will recognize up to 32GB -- but I'm not
>> certain on if 32GB is in fact the upper limit for 64-bit Xen.
>>
>>     
>
> http://www.redhat.com/rhel/compare/
>
> RHEL5 supports 16 GB of mem on x86 (32bit) platform. 
> RHEL5 supports 256 GB of mem on x86_64 platform.
>
> And RHEL5 contains Xen.
>
> http://www.nabble.com/Unable-to-start-hvm-guest-on-cs16998-td15419631.html
>
> "Running Xen Unstable changeset 16998 (pulled  20080208) on Unisys ES7000/one 64x 256gb with SLE10SP1 x64."
>
> There you have an actual server with 256 GB of mem running Xen :) 
>
> (yeah, the mail is about problems, but hey, it's xen-unstable repository
> they're testing there :)
>
> -- Pasi
>   


-- 
Joshua West
Systems Engineer
Brandeis University
http://www.brandeis.edu

Re: Hypervisor Memory Limitations on 64-bit Architecture?

[Konrad Rzeszutek]

> http://www.redhat.com/rhel/compare/
> 
> RHEL5 supports 16 GB of mem on x86 (32bit) platform. 
> RHEL5 supports 256 GB of mem on x86_64 platform.

Actually in RHEL5 U2 it can do 512GB on x86_64 platforms. Check this out:

http://lists.xensource.com/archives/html/xen-devel/2007-11/msg00616.html
(The bug-fix for this isn't mentioned in the release notes - not sure why
thought)