Clustered VMs - High Availability vs Fault Tolerance

Discussion in 'Clustering' started by Dean Powell, May 7, 2010.

  1. Dean Powell

    Dean Powell Guest

    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

    Thanks. Dean
    Dean Powell, May 7, 2010
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  2. Dean Powell

    RCan Guest

    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.

    RCan, May 7, 2010
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  3. This is the expected behaviour.
    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.
    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:

    I hope it helps.

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

    Russ Kaufmann, May 9, 2010
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