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Re: [Xen-devel] (strange idea) unfriendly migration

To: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] (strange idea) unfriendly migration
From: George Shuklin <george.shuklin@xxxxxxxxx>
Date: Tue, 02 Nov 2010 00:43:43 +0300
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В Пнд, 01/11/2010 в 10:15 +0000, Tim Deegan пишет:
> Hi,
> At 20:07 +0100 on 29 Oct (1288382841), George Shuklin wrote:
> > Good day.
> > 
> > As we all know, xen requires assist from VM to migrate it. If VM will
> > acts wrong during migration, it will crash, or behave strangely until
> > reboot (nice sample - default -xen kernel in lenny).
> > 
> > We need to accept changes in domU during migration: other domain id,
> > new vbd/vif and so on.
> > 
> > This fine until we talks about friendly VM. But if VM is not very
> > friendly? For example, VM's user can upgrade kernel to different -xen,
> > which one working fine with normal mode, but incompatible with
> > migration? (Pretty typical situation for any kind of cloud environment
> > or hosting).
> The user can break their VM's kernel in all sorts of other ways too. :)
> > If we create HVM-based overlay for PV-guest to keep thing unchanged, we
> > can make migration much simpler.
> Nice idea.  I'm not sure it's better than just using HVM for the guest
> in the first place, though - that way the user can install pretty much
> any kernel they want.  And the performance would be worse than either
> plain PV or plain HVM.

Well... Reason I'm takling about such strange solution is many broken
kernels for xen in debian, for example. They works fine and user have no
real intention to broke VM (dd from /dev/zero to root will be more
effective), but update distributive without any bad intention...

HVM have other problem: they do not allow to account disk/network
operation without PV_drivers....

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