Re: [Xen-API] can any one please clarify on this

[Denis Cardon <denis.cardon@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Parker,
>            I am al ittle confused on these terms,can you please help on
> this.
>
>             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
>     
> <http://blogs.citrix.com/2011/08/08/tuning-xenserver-for-maximum-scalability/>
>     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 if is based on 64 bit kernel then why it
> is not able to address more than 4GB for itself.
The Xen hypervisor is 64bit, so that virtual machine can be 32 or 64 
bit. It can only run on 64bit hardware, and xcp iso does not install on 
32 bit machines.
Dom0 is used for management, it displays the screen that gives you the 
xsconsole after boot. Dom0 is 32bit and don't need a lot of RAM. Looking 
at a XCP 1.1 production server with 24GB currently running, the dom0 
memory default is 752MB, and currently 262MB are used (excluding cache). 
It is fixed at boot time in /boot/extlinux.conf (dom0_mem=752M)
Need for ram in dom0 depends on what you'll be doing in there (iscsi, 
monitoring tools, number of vms, etc.), and I've been fine with default 
value up to now. The memory that is not used by dom0 can be allocated to 
virtual machines (in the above case, that means 24GB - 750MB).
Virtual machines, can be either 32bit or 64 bit. If you are using 32bit 
without PAE, then you'll be stuck with 4GB max of RAM.
hope this helps,

Denis


> 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 memory lower than  4 GB only and rest
> of the ram is for assigning  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.
>
>
> Faithfully,
> kevin Parker
>
>
> This body part will be downloaded on demand.

--
Denis Cardon
Tranquil IT Systems
44 bvd des pas enchantés
44230 Saint Sébastien sur Loire
tel : +33 (0) 2.40.97.57.57
http://www.tranquil-it-systems.fr


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