Re: [Xen-users] HA Xen on 2 servers!! No NFS, special hardware, DRBD or iSCSI...

[Michael Paesold <mpaesold@xxxxxx>]

Chris de Vidal wrote:
> Reflecting upon this some more, I think perhaps it could be done in Dom0, 
> making setting up
> software RAID inside the DomUs unnecessary.  But that requires a shared 
> hardware-like setup.  DRBD
> 0.7 doesn't allow primary/primary (equivalent to shared hardware) but things 
> like AoE do (NBD
> should, too).  When DRBD 0.8 becomes more stable and primary/primary is 
> possible, perhaps that
> will be an option.  I like the DRBD project and would be eager to try it.
>
> As Eric said, using AoE means any network interruption generates a resync.  But 
> then that's a
> concern with /ANY/ AoE or iSCSI + software RAID setup.  So methinks AoE isn't 
> too bad.  Add in the
> fr1 patch and it might be usable.
>
> If one were to patch the kernel with the "Fast RAID" patch and use AoE to 
> create /dev/md0 on Dom0
> using both a local disk and a remote, this might work!  In this case, LVM would 
> no longer be a
> necessity.
It can't see how this should work with RAID in Dom0. At that point you 
are just at the same problem as with DRBD. During live migration, you 
would first have to deactivate the RAID on the first node and only then 
activate it on the second node.
But for live migration to work, both need to be active for a short 
period of time.
I wonder if anyone will ever step up and create a patch to xend that 
makes it possible to do live migration without having a storage setup 
that can be active at two nodes, i.e. suspend -> disconnect storage -> 
connect storage on second node -> resume on second node. I am really 
sorry I have no time to do it myself.
> Does anyone know if Xen's live migration requires something like GFS
> on shared hardware?  Or does
> it take care of the problem as long as it's the only thing accessing
> the drive?

Only one node must access the device at a time. But for your 
RAID-in-dom0 idea, that is not the case.
Best Regards,
Michael Paesold






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