Re: [Xen-users] HVM vs PV (Xen Full virtualization (HVM) Xen Paravirtualization (PV))

[nemus@xxxxxxxxxxxxxxx]

Thank you for the reply.

So the debate I have been having is. Even with the new cpu technology that
helps out the virtualization PV is still a better option right?

So if you had a choice between hvm and pv you should using pv because it
will have an over all better performance.

Is that correct?

Thank you.

> Hi Nemus!
>
>  I have talked about this last week in a XenServer lecture.
>
>  1- HVM domains are based on a emlulation of the hardware writen entirely
> in
> software (a.k.a. QEmu) and it depends on a assistence by hardware to
> become
> useful.
>
>  2- PVM domains are the new approach of virtualization technique, simple
> there is no "hardware emulation via software" within a PVM domain. No
> emulation at all. It is much more fast!! You just need a old 64Bits CPU to
> virtualize Linux, some BSDs and OpenSolaris using PVM domains.
>
> Try this:
>
>  Install two Debians in your XenServer, one HVM and another PVM:
>
>  1- Debian HVM (hostname debian01), at XenCenter click "New VM", select
> "Other Install media" and choose the original Debian ISO CD image from
> your
> "NFS ISO storage repository";
>
>  2- Debian PVM (hostname debian02), at XenCenter click "New VM", select
> "Debian Squeeze 6 32 bits", choose the "Install URL" method and type "
> http://ftp.debian.org/debian/";, configure the network within the VM
> (better
> with dhcp server on your network) and install it normally.
>
>  After that, you will be able to see the big differences from debian01
> (HVM)
> to debian02 (PVM) with one Linux command:
>
>
> * HVM Domain has a *virtual* motherboard, plus *virtual* PCI devices as:
> IDE/SCSI block devices, hard disc, video board, *all emulated by
> software*:
>
> username@debian01~$ lspci
> <YOUR EMULATED PCI DEVICES LISTED HERE>
>
>
> * PVM Domain have no virtual motherboard or any virtual PCI devices
> (notthing will appear because there is nothing to show):
>
> username@debian02~$ lspci
> username@debian02~$
>
>
>  As you'll figure out, emulation tasks are heavy and slow, the emulation
> is
> expensive and a slow proccess, but recently Intel and AMD implemented an
> assistance for hardware emulation within their CPUs in order to make it
> feasible to emulation
>
>  The disk and network within a PVM domain is just some frontends
> (blockfront
> and netfront), that talsk directily to the dom0 (blockback and netback),
> without any emulation.
>
>  Also, it is possible to convert a VM from HVM to PVM after the
> installation, and vice-versa.
>
>  Windows does not work as a PVM domain.
>
> Att,
> Thiago
>
> On 5 May 2011 16:40, <nemus@xxxxxxxxxxxxxxx> wrote:
>
>> Is HVM or PV better for performance and overall stability in xen?
>>
>> I asked on Linux question but got mixed results.
>>
>>
>> http://www.linuxquestions.org/questions/linux-virtualization-90/hvm-vs-pv-xen-full-virtualization-hvm-xen-paravirtualization-pv-872427/
>>
>>
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>>
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