On 02/14/2012 08:32 PM, Itamar Heim wrote:
On 02/14/2012 06:31 PM, Adam Litke wrote:
On Thu, Feb 09, 2012 at 11:45:09AM -0500, Perry Myers wrote:
warning: tl;dr
Right now, HA in oVirt is limited to VM level granularity. Each VM
provides a heartbeat through vdsm back to the oVirt Engine. If that
heartbeat is lost, the VM is terminated and (if the user has configured
it) the VM is relaunched. If the host running that VM has lost its
heartbeat, the host is fenced (via a remote power operation) and all HA
VMs are restarted on an alternate host.
Has anyone considered how live snapshots and live block copy will
intersect HA
to provide a better end-user experience? For example, will we be able
to handle
a storage connection failure without power-cycling VMs by migrating
storage to a
failover storage domain and/or live-migrating the VM to a host with
functioning
storage connections?
Not sure I get the scope here - if the storage is dead, the VM won't be
able to copy the storage to its new destination. There is only one
theoretical chance it will work - for shared storage, if one of the
hosts has its hba/nic/link/port dead maybe some other host will be able
to access the storage. It seems like a long shot to me. More over,
not all of the guest IO reached the storage prior to the migration. Even
w/ ODIRECT there is still various caches around, some belong to the VM,
some may be meta data for image files. We won't be able to switch to
another host w/o writing the data in most cases.
cc'ing Dor - iirc, he mentioned an issue with live migrating a guest
post an IO error
In short, while it may be theoretically possible in rare cases, I rather
not to relay on it. Seems that the 'average' storage array/HBA is more
stable than live migration + IO errors path...
Cheers,
Dor
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