[Xen-users] multiple dom0s (was: Re: [Xen-devel] ragarding xen in sles10)

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

Hi Namitha,

I hope you don't mind but I've copied my reply onto xen-users for public 
visibility.

> I am trying to create two privileged domains for better performance.....
> I have set up XEN on sles10 sp1. Created VMs on that.
>
> Is it possible to create two domain0's? If it is possible how can we
> make them to manage VMs.
>
> I tried a lot to get document on such topics...but I failed to get such
> document.

dom0 is much like a domU but it is special in a number of ways.  Two important 
ways are:

1) can access the real hardware - by default dom0 owns all the real hardware 
in the system
2) can manage other domains

Number 1 can be extended to domUs using the pciback / pcifront drivers.  This 
allows you to dedicate PCI devices to PV domUs.  If you want, you can set 
these domUs to be "backends" for certain devices, so that they export their 
devices as virtual disks or virtual network interfaces to other domUs, just 
like dom0 does.  Or they can just use the devices themselves to improve 
performance.  Giving a domain this ability means that you are trusting it as 
much as dom0.

A more restricted form of this would be to just dedicate, say, a serial port 
to a domain.  There's basic support so that HVM domains can be given 
dedicated access to USB devices.  And in the xen-unstable tree it's now 
possible to dedicate PCI devices to HVM domUs - and isolate them so they 
can't damage the system.

Number 2 is currently reserved only for dom0 and there's no way of allowing 
another domain to share this function.

There are lots of possibilities here, depending on what you're trying to 
achieve.

Cheers,
Mark

>
> -----Original Message-----
> From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On Behalf Of Mark
> Williamson
> Sent: Monday, 3 December 2007 9:26 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: P, Namitha
> Subject: Re: [Xen-devel] ragarding xen in sles10
>
> Hi there,
>
> If you google around a bit you may find some backup scripts that people
> have
> hacked up...  I can't think of a specific project you'd go to off the
> top of
> my head.
>
> > I am new to xen . I need to develop one project that will back up
> > virtual machine from host. Is there any "script which will support
>
> this"
>
> > in host. Or any script which is used to list files of virtual machines
> > in the host..........please help me in this regards
>
> You could parse the config file to figure out what disk files are used
> by the
> VM.  Or you could use the xenstore-* (e.g. xenstore-ls) commands to read
>
> details from Xenstore regarding what the paths of the virtual disks are.
>
> Or, more simply, you could just adopt a naming strategy for your
> domain's
> virtual disks based on their config file name / hostname.  And then just
> code
> your backup scripts to understand that (e.g. domain with "hostname" has
> config file /etc/xen/hostname and disk /vm-disks/hostname.disk).  It'll
> be
> site-specific but if it works for you, that's what counts.
>
> Personally, I just rsync backup the contents of /mnt/vm/, which contains
> all
> my VM's virtual disks (having shut the VMs down first).  I also
> rsync /etc/xen/ to my backup device.  This doesn't record which disk
> belongs
> to which VM but it does make it easy to restore the whole lot at once
> (just
> rsync them back).  If I ever need to restore a particular VM I can do it
>
> manually without to much hassle.
>
> Actually, I've been working on a much more advanced backup script for
> backing
> up VMs in a home / smaller deployment environment.  I'm waiting on word
> from
> my employers regarding whether I can release this publically.  For
> anyone
> interested, there's some details at
> http://www.cl.cam.ac.uk/~maw48/vm-backup-pictures/ - but don't hold your
>
> breath for it to be released because it could take a long while to get
> permission, if it's allowed at all.
>
> Cheers,
> Mark



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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