Poweredge 1850 - 4GB RAM

Poweredge 1850 - 4GB RAM

[Brian Hays]

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Hello,

Has anyone tried the current stable Xen with a Poweredge 1850 w/ 4GB ram? I 
know that without PAE Xen can't support more than 4GB on a system, but I've 
seen some results posted on the list that sometimes even 4GB will only show 
up as 3.3GB or 3.5GB in Xen. Does anyone know if the full 4GB will show as 
available on the 1850?

Thanks,
Brian

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Re: Poweredge 1850 - 4GB RAM

[Fajar A. Nugraha]

Brian Hays wrote:

> Hello,
>
> Has anyone tried the current stable Xen with a Poweredge 1850 w/ 4GB 
> ram? I know that without PAE Xen can't support more than 4GB on a 
> system, but I've seen some results posted on the list that sometimes 
> even 4GB will only show up as 3.3GB or 3.5GB in Xen. Does anyone know 
> if the full 4GB will show as available on the 1850?
>
On my experince with IBM HS20, Xeon EM64T, only Linux with PAE can 
detect full 4GB. Linux without PAE only detects 3.5 GB. I suspect this 
is also the case for Xen.

Regards,

Fajar

RE: Poweredge 1850 - 4GB RAM

[Petersson, Mats]

> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com 
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
> Fajar A. Nugraha
> Sent: 09 September 2005 08:20
> To: xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] Poweredge 1850 - 4GB RAM
> 
> Brian Hays wrote:
> 
> > Hello,
> >
> > Has anyone tried the current stable Xen with a Poweredge 
> 1850 w/ 4GB 
> > ram? I know that without PAE Xen can't support more than 4GB on a 
> > system, but I've seen some results posted on the list that 
> sometimes 
> > even 4GB will only show up as 3.3GB or 3.5GB in Xen. Does 
> anyone know 
> > if the full 4GB will show as available on the 1850?
> >
> On my experince with IBM HS20, Xeon EM64T, only Linux with 
> PAE can detect full 4GB. Linux without PAE only detects 3.5 
> GB. I suspect this is also the case for Xen.

Yes, that would be what one can expect. Without PAE, the address range
of the processor for EVERYTHING is limited to 4GB. In this address
range, you'll find PCI devices that use memory mapped IO, and those will
require a variable amount of memory, but it's likely that there will be
a loss of about 200-800KB due to IO devices that are mapped into the 4GB
memory space. The biggest factor on _HOW MUCH_ of this space is used is
the graphics card, as it can easily take up 256MB of "space".

With PAE, the processes that do not actually touch the real hardware can
have memory from above 4GB mapped to the area that is used by the
hardware, and that is why you'll see ALL of the ram with this option.
[64-bit is essentially using the existing PAE, but extended to support
more bits].

--
Mats
> 
> Regards,
> 
> Fajar
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 

Re: Poweredge 1850 - 4GB RAM

[Mark Williamson]

> Has anyone tried the current stable Xen with a Poweredge 1850 w/ 4GB ram? I
> know that without PAE Xen can't support more than 4GB on a system, but I've
> seen some results posted on the list that sometimes even 4GB will only show
> up as 3.3GB or 3.5GB in Xen. Does anyone know if the full 4GB will show as
> available on the 1850?

It all depends on the hardware.  You'll never get the full 4GB, it's just a 
question of how much your BIOS is wasting.  Some BIOSes use way more machine 
address space than they really need to in order to support memory-mapped IO 
regions.  Some of them are more efficient.

You'll always need PAE enabled to get at all the memory - true whether it's 
Linux or Xen you're running :-(

Cheers,
Mark