Clustered VMs - High Availability vs Fault Tolerance

We have a three node cluster and multiple virtual machines balanced across
the three nodes.

Most are running an application that requires a user initiated telnet
session. On those application service VM's I can Live Migrate and the
connections remain intact. When any other type of failover is attempted the
session is disconnected.

I have found myself in quite a debate regarding the differences between HA
and FT. I don't believe it would be possible to migrate the resource without
an impact to the telnet sessions, outside of live migration. Am I incorrect?

Should I expect to be able to configure a virtual machine in failover
clustering and expect no downtime? If so, can someone explain how that is
possible.

Thanks. Dean

Hi Dean,

I think you are correct, I would call a normal failover as "save state VM +
move LUN/ressource to other node and start it" process. The VM will be
paused here.

A LM is different here, in a LM process the VM will be running and the RAM
state will be migrated to other other node and during the last copy process
of RAM there will be a small timeout, normally (depends on network speed)
within a TCP timeout window. That means your telnet app should stay alive.

Hope that helps.

Regards
Ramazan

"Dean Powell" <> wrote in message
news:E61B5CA4-EAEF-4D26-8A23-...
> We have a three node cluster and multiple virtual machines balanced across
> the three nodes.
>
> Most are running an application that requires a user initiated telnet
> session. On those application service VM's I can Live Migrate and the
> connections remain intact. When any other type of failover is attempted
> the
> session is disconnected.
>
> I have found myself in quite a debate regarding the differences between HA
> and FT. I don't believe it would be possible to migrate the resource
> without
> an impact to the telnet sessions, outside of live migration. Am I
> incorrect?
>
> Should I expect to be able to configure a virtual machine in failover
> clustering and expect no downtime? If so, can someone explain how that is
> possible.
>
> Thanks. Dean

"Dean Powell" <> wrote in message
news:E61B5CA4-EAEF-4D26-8A23-...
> We have a three node cluster and multiple virtual machines balanced across
> the three nodes.
>
> Most are running an application that requires a user initiated telnet
> session. On those application service VM's I can Live Migrate and the
> connections remain intact. When any other type of failover is attempted
> the
> session is disconnected.

This is the expected behaviour.

> I have found myself in quite a debate regarding the differences between HA
> and FT. I don't believe it would be possible to migrate the resource
> without
> an impact to the telnet sessions, outside of live migration. Am I
> incorrect?

Failover clustering is HA. You are right that in HA, when there is a move or
a failover of a resource, clients will lose their connections and will have
to reconnect to the resource after the resource is started on another node.

> Should I expect to be able to configure a virtual machine in failover
> clustering and expect no downtime? If so, can someone explain how that is
> possible.

In Live Migration, the resources (VMs) are moved with the memory on the
active location being copied live during the move process. For more info, I
recommend the following site:
http://www.microsoft.com/downloads/d...displaylang=en

I hope it helps.

--
Russ Kaufmann
MVP, MCT, MCITP x7, MCTS x9, MCSE x4, CTT+
ClusterHelp.com, a Microsoft Gold Certified Partner

Email:
http://www.clusterhelp.com
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