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Old 06-15-2008, 10:45 PM
Luke S Crawford
 
Default Centos 5.2 and Xen

Ruslan Sivak <russ@vshift.com> writes:
> > running vmware under a xenU guest wouldn't lift any ram limit
> > imposed by the xen kernel or dom0.

...

> The 4GB limit is artificial, and only applies to the vm's started
> using their closed source XenSource. The host OS is most likely
> CentOS 5, and sees the whole 8GB (although it's not x64, so I'm
> guessing they use PAE or something.)

It is PAE.

> I only need 8GB of ram support, and no other features that are offered
> in XenStandard, so it seems kind of a waste to pay $1k per server for
> that. If another virtualization technology was installed on that OS,
> you can get the use of the other 4GB, and if not, I can always run my
> apps on Dom0, although I'd prefer to not install too much stuff on
> Dom0.

First, The Dom0 OS runs as a guest of the Xen hypervisor- it is just
a guest that happens to have access to the PCI bus as well. The Xen
hypervisor still controls what ram and CPU all domains including the Dom0,
can see; if the xen kernel is limiting you to 4G ram total, that
limit will apply in the Dom0 as well.

Also, you are not going to be able to run a virtualization technology that
uses the hardware virtualization support from within a Xen guest, even
if that Xen guest happens to be the Dom0. The Xen hypervisor
controls access to those instructions.

You can run virtualization technologies that don't require HVM- OpenVZ and
linux vserver will both work fine. Heck, you can do that within an
unprivileged Xen DomU, but that won't help you if you want to run
windows.



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Old 06-16-2008, 01:59 AM
Ruslan Sivak
 
Default Centos 5.2 and Xen

Luke S Crawford wrote:

Ruslan Sivak <russ@vshift.com> writes:


running vmware under a xenU guest wouldn't lift any ram limit
imposed by the xen kernel or dom0.



...



The 4GB limit is artificial, and only applies to the vm's started
using their closed source XenSource. The host OS is most likely
CentOS 5, and sees the whole 8GB (although it's not x64, so I'm
guessing they use PAE or something.)



It is PAE.


If it's PAE, then I'm a bit confused, as they advertise it as "*Native
64-bit hypervisor:* Scalability and support for enterprise applications"

I only need 8GB of ram support, and no other features that are offered
in XenStandard, so it seems kind of a waste to pay $1k per server for
that. If another virtualization technology was installed on that OS,
you can get the use of the other 4GB, and if not, I can always run my
apps on Dom0, although I'd prefer to not install too much stuff on
Dom0.



First, The Dom0 OS runs as a guest of the Xen hypervisor- it is just
a guest that happens to have access to the PCI bus as well. The Xen
hypervisor still controls what ram and CPU all domains including the Dom0,
can see; if the xen kernel is limiting you to 4G ram total, that
limit will apply in the Dom0 as well.


Also, you are not going to be able to run a virtualization technology that
uses the hardware virtualization support from within a Xen guest, even
if that Xen guest happens to be the Dom0. The Xen hypervisor
controls access to those instructions.


You can run virtualization technologies that don't require HVM- OpenVZ and
linux vserver will both work fine. Heck, you can do that within an
unprivileged Xen DomU, but that won't help you if you want to run
windows.


Well I have up to 4GB of run windows and I can have the other 4GB for
dom0, so if I can get OpenVZ or linux vserver running on there, I can
use that to run my linux VM's.

Doesn't openVZ require a different kernel? That would replace the Xen
kernel wouldn't it? Or is there a way to custom compile Xen+OpenVZ kernel?


I'm not too familiar with linux vserver, but my guess is you can't run
it in Dom0 either...


Russ


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Old 06-18-2008, 05:09 AM
Luke S Crawford
 
Default Centos 5.2 and Xen

Ruslan Sivak <russ@vshift.com> writes:

> Luke S Crawford wrote:
> > It is PAE.

> If it's PAE, then I'm a bit confused, as they advertise it as "*Native
> 64-bit hypervisor:* Scalability and support for enterprise
> applications"

heh. looks like I wasn't paying attention. A long time ago, I believe the
xensource product (3.1?) was i386-PAE only- and 32-on-64 is 32-PAE
on 64, so you won't be able to run non-pae 32-bit guests in paravirt
mode.

> Well I have up to 4GB of run windows and I can have the other 4GB for
> dom0, so if I can get OpenVZ or linux vserver running on there, I can
> use that to run my linux VM's.

But xenexpress limits you to 4Gb of physical ram total
see http://www.xensource.com/Documents/XenServer41ProductOverview.pdf
so if you have 4Gb in the DomU, you can't use another 4Gb in the Dom0

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Old 06-18-2008, 01:30 PM
Ruslan Sivak
 
Default Centos 5.2 and Xen

Luke S Crawford wrote:

Well I have up to 4GB of run windows and I can have the other 4GB for
dom0, so if I can get OpenVZ or linux vserver running on there, I can
use that to run my linux VM's.



But xenexpress limits you to 4Gb of physical ram total
see http://www.xensource.com/Documents/XenServer41ProductOverview.pdf
so if you have 4Gb in the DomU, you can't use another 4Gb in the Dom0


_______________________________________________



From what I understand, they limit you to 4GB for DomU, you still have
another 4GB available for Dom0, that you can use to run other apps,
including possibly QEMU, or some other virtualization products.


Russ
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Old 06-23-2008, 12:32 PM
Tom Lanyon
 
Default Centos 5.2 and Xen

On 18/06/2008, at 11:00 PM, Ruslan Sivak wrote:

From what I understand, they limit you to 4GB for DomU, you still
have another 4GB available for Dom0, that you can use to run other
apps, including possibly QEMU, or some other virtualization products.


Russ



I haven't been following the thread, but has the discussion been about
memory limits of Xen?


Am I going to face any issues wanting to run some CentOS 5.x x86_64
boxes with 16 or 32 GB memory as Xen hosts with up to 10 or 12 GB
memory CentOS 5.x x86_64 domUs ?


Furthermore, am I going to encounter issues running CentOS 5.x i386
boxes with 8 GB memory trying to run CentOS 4.x i386 domUs with 3.5 or
4GB memory?



Regards,
Tom
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Old 06-23-2008, 11:38 PM
Luke S Crawford
 
Default Centos 5.2 and Xen

Tom Lanyon <tom@netspot.com.au> writes:
> I haven't been following the thread, but has the discussion been about
> memory limits of Xen?

We were discussing memory limits of the free (as in beer) closed source
citrix xensource product- limits are added to the free product in order
to encourage people to upgrade to the more expensive products.

These limits don't exist in the open-source xen product, which is what
the centos/Xen stuff is based on.

http://tx.downloads.xensource.com/downloads/docs/user/#SECTION01130000000000000000

> Am I going to face any issues wanting to run some CentOS 5.x x86_64
> boxes with 16 or 32 GB memory as Xen hosts with up to 10 or 12 GB
> memory CentOS 5.x x86_64 domUs ?

I've personally run CentOS x86_64 5.1 boxes with north of 16G ram-
there is nothing I am aware of that would stop you from putting as much
ram as you want in a particular DomU.

> Furthermore, am I going to encounter issues running CentOS 5.x i386
> boxes with 8 GB memory trying to run CentOS 4.x i386 domUs with 3.5 or
> 4GB memory?

You will be needing PAE, but that is default for CentOS i386/xen, so it
should Just Work. make sure you install the libc6-xen package (should
be installed as a dependency.) The usual PAE limits apply.

I'm typing this message in emacs running on a DomU hosted on an i386/PAE box
with 6G ram running CentOS5.1/xen.

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Old 06-24-2008, 12:53 AM
Tom Lanyon
 
Default Centos 5.2 and Xen

On 24/06/2008, at 9:08 AM, Luke S Crawford wrote:
We were discussing memory limits of the free (as in beer) closed
source
citrix xensource product- limits are added to the free product in
order

to encourage people to upgrade to the more expensive products.

These limits don't exist in the open-source xen product, which is what
the centos/Xen stuff is based on.

http://tx.downloads.xensource.com/downloads/docs/user/#SECTION01130000000000000000

I've personally run CentOS x86_64 5.1 boxes with north of 16G ram-
there is nothing I am aware of that would stop you from putting as
much

ram as you want in a particular DomU.

You will be needing PAE, but that is default for CentOS i386/xen, so
it

should Just Work. make sure you install the libc6-xen package (should
be installed as a dependency.) The usual PAE limits apply.

I'm typing this message in emacs running on a DomU hosted on an i386/
PAE box

with 6G ram running CentOS5.1/xen.



Hi Luke,

Thanks for the confirmation; this is what I had understood but some of
the prior discussion scared me.


Regards,
Tom
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Old 06-24-2008, 02:09 AM
Ruslan Sivak
 
Default Centos 5.2 and Xen

Tom Lanyon wrote:

On 24/06/2008, at 9:08 AM, Luke S Crawford wrote:

We were discussing memory limits of the free (as in beer) closed source
citrix xensource product- limits are added to the free product in order
to encourage people to upgrade to the more expensive products.


From what I understand, Citrix does provide source to their product, so
other then licensing, how is it different from open source?


Russ
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Old 06-24-2008, 02:30 AM
"Adriano dos Santos Vieira (Hapia IN)"
 
Default Centos 5.2 and Xen

Hi, guys!

Please, could I ask you by some documentation about XEN and Cluster on
CEntOS-5. Theese one could be from basic to advanced level.

Thanks in advance.

Adriano Vieira
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Old 06-24-2008, 09:43 AM
Ralph Angenendt
 
Default Centos 5.2 and Xen

Adriano dos Santos Vieira (Hapia IN) wrote:
> Hi, guys!
>
> Please, could I ask you by some documentation about XEN and Cluster on
> CEntOS-5. Theese one could be from basic to advanced level.

<http://www.centos.org/docs/5/>

Not that hard to find.

Ralph
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