As per XCP documentation, Xen Cloud Platform host is a 64 bit x86 server-class machine devoted to hosting multiple VMs.

on blog.citrix.com they are mentioning about dom0 as It should be noted that dom0 is a 32-bit process

i am little bit confused over these facts what is host and dom0 mentioning here.I thought dom0 is a 32 bit centos kernel and does host means xen hypervisor?

if host means hypervisor which is based on 64 bit kernel then why it is not able to address more than 4GB for itself.

Also How is the 32 bit kernel of dom0 depends on assigning more ram to xen server/XCP(on citrix blog they are telling since dom0 is based on 32 bit kernel xen server can have maximum of 4 gb only and rest of the ram for assigning to vms,also if we assign more than 4GB xen server will fail!!).

From my understanding dom0 provides an interface to manage VM and xen.Can anyone please give me a simple explanation to this.


Both are correct,whats the need of confusion here.

Xen hypervisor used on XCP is 64 bit and hence it can create both 32 bit and 64 bit guests.

Dom0 which is actually another VM running on top of xen hypervisor is 32 bit and is mainly for providing disk and network access to DomU.

Dom0 does not determine RAM,for your host.

You can even specify how much ram Dom0 can have using dom0_mem= in /boot/extlinux.conf.

To see total available memory use

 xl info |grep total_memory

free -m

on dom0 is actually showing ram assigned to dom0 and not to xen hypervisor.


See this part of the article from the link you mentioned,

When a host running XenServer starts up, the Xen hypervisor loads a small
virtual machine that is essentially invisible to users (and even admins
if you don’t know where to look!).  This special, privileged VM is referred
to as the “control domain”, “domain-0” or, as the cool kids like to call it,
“dom0”. The control domain runs the management tool stack and also provides
low-level services to other VMs, such as providing physical access to devices.

and this


As long as you have a 64bit hardware and hypervisor, 32bit dom0 does not matter and you can assign as much memory as you want to your 64 bit guests. dom0 is only used to "manage" hardware and provide low level services to the guests. It does not interfere in the operation or memory allocation to the guests.

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    Actually i need to assign 24 Gb RAM to my host so that i can utilize shared memory for running vm on ram..But i dont understand why dom0 determines ram for the host. – Blue Gene Aug 22 '12 at 15:36

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