Re: [Xen-users] iscsi vs nfs for xen VMs

[Adi Kriegisch <adi@xxxxxxxxxxxxxxx>]

Hi!

> >> With that setup, are you able to do live migration ?
> >
> > no he cannot
> >
> > he can do live migration if he make the raid1 inside domus
[SNIP]
> 
> Why not?
> 
> Live migration only relies on shared storage on the dom0, not on the domU
Right... The part of "storage" you need to share is whatever you export to
your domU. So if you use something like:
   (...)
   'phy:/dev/my-cool-volume-group/server-disk,xvda1,w'
   (...)
you need to take care that the very same disk exists on every single dom0
participating in this cluster. In case you want to use software RAID your
DomU config looks like this:
   (...)
   'phy:/dev/md10,xvda1,w'
   (...)
So /dev/md10 needs to be available on all dom0 -- which isn't, of course...

As a side note: I never tried this and I would NOT recommend to ever use
that, but it could be possible to do such crazy stuff: If you can ensure
that only one domU has access to a device and you somehow manage to make
RAID device names unique within your cluster and you can ensure that no
dom0s have any of those RAID monitoring jobs running then it could work (at
least for some time) -- but it is pointless, as you have no control
whatsoever over your raid devices, there is no monitoring at all and in
case you need to rebuild, you need to carefully check on which host you'll
do it... Ah, and upgrades of <your-favorite-distro> will be pretty hard to
do as you need to stop [pre|post]-upgrade scripts from snapping in and
touching your RAID devices.

-- Adi

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