1:34 p.m.
Hello,
I was testing put host into maintenance on 4.0.6, with 1 VM running.
It correctly completes the live migration of the VM and I see this event in
pane:
Migration completed (VM: ol65, Source: ovmsrv06, Destination: ovmsrv05,
Duration: 39 seconds, Total: 39 seconds, Actual downtime: 133ms)
What is considered as "Actual downtime"?
Thanks,
Gianluca
1:49 p.m.
Hi Gianluca,
My educated guess...When you live migrate a VM, its state in memory is
copied over to the new host, but the VM still remains online during this
period to minimise downtime. Once its state in memory is fully copied to
the new host, the VM is paused on the original host, its memory
resynchronised one last time & then brought up on the new host.
So whilst the entire process took 39 seconds, actual downtime was only
133ms.
Doug
On 27 January 2017 at 09:34, Gianluca Cecchi <gianluca.cecchi(a)gmail.com>
wrote:
Hello,
I was testing put host into maintenance on 4.0.6, with 1 VM running.
It correctly completes the live migration of the VM and I see this event
in pane:
Migration completed (VM: ol65, Source: ovmsrv06, Destination: ovmsrv05,
Duration: 39 seconds, Total: 39 seconds, Actual downtime: 133ms)
What is considered as "Actual downtime"?
Thanks,
Gianluca
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--
Doug
1:59 p.m.
its memory resynchronised one last time
Actually, thinking about it, rather than diffing *all* of the memory on the
first host to resync it at the last moment, the hypervisor probably
simultaneously copies the current state of memory & uses copy-on-write
(COW) to write all new transactions to both hosts.
Only a technical difference, but it'd greatly reduce how long the VM needs
to be paused to complete a full sync.
--
Doug
8:31 a.m.
On Fri, Jan 27, 2017 at 2:59 PM, Doug Ingham <dougti(a)gmail.com> wrote:
> its memory resynchronised one last time
Actually, thinking about it, rather than diffing all of the memory on the
first host to resync it at the last moment, the hypervisor probably
simultaneously copies the current state of memory & uses copy-on-write (COW)
to write all new transactions to both hosts.
Only a technical difference, but it'd greatly reduce how long the VM needs
to be paused to complete a full sync.
Is this in 4.1? See also:
http://www.ovirt.org/develop/release-management/features/migration-enhanc...
Best,
--
Didi
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3 comments
3 participants
participants (3)
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Doug Ingham -
Gianluca Cecchi -
Yedidyah Bar David