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Adding Eli.<br>
<br>
<br>
<div class="moz-cite-prefix">On 01/27/2014 02:50 PM, Andrew Lau
wrote:<br>
</div>
<blockquote
cite="mid:CAD7dF9fNhvSsd+Oj2s+rJo4oSkwnZiU6H23tbY0XL12_JShfsw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_default" style="font-family:tahoma,sans-serif">Hi,</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif"><br>
</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif">
I think he was asking what if the power management device
reported that the host was powered off. Then VMs should be
brought back up as being off would essentially be the same as
running a power cycle/reboot?</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif">
<br>
</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif">Another
example I'm seeing is what happens if the whole host loses
power and it's power management device then becomes
unavailable (ie. not reachable) then you're stuck in the case
where it requires manual intervention. </div>
<div class="gmail_default" style="font-family:tahoma,sans-serif"><br>
</div>
<div class="gmail_default" style="font-family:tahoma,sans-serif">I
would be interested to potentially see something like a
timeout on those problematic VMs (eg. if nothing was read or
write after x amount of time) then you could consider the host
as offline? I guess then that adds a lot of risk..</div>
<div class="gmail_extra">
<br>
<br>
<div class="gmail_quote">On Mon, Jan 27, 2014 at 11:43 PM,
Tareq Alayan <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:talayan@redhat.com" target="_blank">talayan@redhat.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<br>
<br>
Power management makes use of special *dedicated* hardware
in order to restart hosts independently of host OS. The
engine connects to a power management devices using a
*dedicated* network IP address.<br>
The engine is capable of rebooting hosts that have entered
a non-operational or non-responsive state,<br>
The abilities provided by all power management devices
are: check status, start, stop and recycle (restart)...<br>
<br>
In the case of non-responsive host: all of the VMs that
are currently running on that host can also become
non-responsive. However, the non-responsive host keeps
locking the VM hard disk for all VMs it is running.
Attempting to start a VM on a different host and assign
the second host write privileges for the virtual machine
hard disk image can cause data corruption.<br>
Rebooting allows the engine to assume that the lock on a
VM hard disk image has been released.<br>
The engine can know for sure that the problematic host has
been rebooted via the power management device and then it
can start a VM from the problematic host on another host
without risking data corruption.<br>
Important note: A virtual machine that has been marked
highly-available can not be safely started on a different
host without the certainty that doing so will not cause
data corruption.<br>
<br>
N-joy,<br>
<br>
--Tareq
<div class="HOEnZb">
<div class="h5"><br>
<br>
<br>
<br>
On 01/27/2014 02:05 PM, Dafna Ron wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I am adding Tareq for the Power Management
implementation.<br>
<br>
Dafna<br>
<br>
<br>
On 01/27/2014 11:48 AM, Karli Sjöberg wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
On Mon, 2014-01-27 at 11:11 +0000, Dafna Ron
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0
0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
Powering off the host will never trigger vm
migration.<br>
As far as engine is concerned it just lost
connection to the host, but<br>
has no way of telling if the host is down or if
a router is down.<br>
</blockquote>
Can´t it at least check with power management if
the Host status is down<br>
first?<br>
<br>
I mean, if the network is down there will be no
response from either PM<br>
or Host. But if PM is up and can tell you that the
Host is down, sounds<br>
rather clear cut to me...<br>
<br>
Seems to me the VM's would be restarted sooner if
the flow was altered<br>
to first check with PM if it´s a network or Host
issue, and if Host<br>
issue, immediately restart VM's on another Host,
instead of waiting for<br>
a potentially problematic Host to boot up
eventually.<br>
<br>
/K<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0
0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
since vm's can continue running on the host even
if engine has no access<br>
to it, starting the vm's on the second host can
cause split brain and<br>
data corruption.<br>
<br>
The way that the engine knows what's going on is
by sending heath check<br>
queries to the vdsm.<br>
Power management will try to reboot a host when
the health checks to<br>
vdsm will not be answered.<br>
So... if engine gets no reply and has no way of
rebooting the host, the<br>
host status will be changed to Non-Responsive
and the vm's will be<br>
unknown because engine has no way of knowing
what's happening with the<br>
vm's.<br>
Since reboot of the host will kill the vm's
running on it - this will<br>
never cause any vm migration but... along with
the High-Availability vm<br>
feature, you will be able to have some of the
vm's re-started on the<br>
second host after the host reboot (and that is
only if Power Management<br>
was confirmed as successful).<br>
<br>
VM migration is only triggered when:<br>
1. Cluster configuration states that the vm
should be migrated in case<br>
of failure<br>
2. Engine has access to the host - so the
failure is on the storage side<br>
and not the host side.<br>
3. the vms are not actively writing (although
there might be a new RFE<br>
for it).<br>
<br>
hope this clears things up<br>
<br>
Dafna<br>
<br>
<br>
<br>
On 01/27/2014 10:11 AM, Andrew Lau wrote:<br>
<blockquote class="gmail_quote" style="margin:0
0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
Hi,<br>
<br>
Have you got power management enabled?<br>
<br>
That's the fencing feature required for the
engine to ensure that the<br>
host is actually offline. It won't resume any
other VMs to prevent<br>
potential VM corruption (eg. VM running on
multiple hosts).<br>
<br>
Andrew.<br>
<br>
On Jan 27, 2014 5:12 PM, "Jaison peter" <<a
moz-do-not-send="true"
href="mailto:urotrip2@gmail.com"
target="_blank">urotrip2@gmail.com</a><br>
<mailto:<a moz-do-not-send="true"
href="mailto:urotrip2@gmail.com"
target="_blank">urotrip2@gmail.com</a>>>
wrote:<br>
<br>
Hi all ,<br>
<br>
I was setting a two node ovirt cluster
with ovirt engine on<br>
seperate node . I completed the
configuration and tested VM live<br>
migrations with out any issues . Then for
checking cluster HA I<br>
powered down one host and expected vms
running on that host to be<br>
migrated to the other one . But nothing
happened , Engine detected<br>
host as un-rechable and marked it as
non-operational and vm ran on<br>
that host went to 'unknown state' . Is
that not possible to setup<br>
a fully HA ovirt cluster with two nodes ?
or else is that my<br>
configuration problem ? please advice .<br>
<br>
Thanks & Regards<br>
<br>
Alex<br>
<br>
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<br>
-- <br>
Dafna Ron<br>
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