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Quorum disk or not? RRS feed

  • Question

  • Hi,

    I'm planning to build a two node hyper-v r2 cluster. The nodes will run Hyper-V r2 server.

    I have a SAN and will use CSV.

    With CSV do I still need a quorum disk?

    Wednesday, May 19, 2010 12:18 PM

Answers

  • Hi Mark,

    You will always need a quorum disk because this is the cluster’s configuration database.

    We can say that the quorum has two very important jobs:

    • First of all, it tells the cluster which node should be active. The quorum tells the cluster which node is currently active
      and which node or nodes are in stand by.
    • Second of all, the quorum intervenes when communications fail between nodes.

     

    So the response is yes Mark ... :)

    Hope to help you.


    David LACHARI
    Wednesday, May 19, 2010 2:12 PM
  • As David states, a cluster always needs some type of quorum.

    The quorum is the recording system of a cluster - it is how the cluster knows what is happening, what is in process, etc.  It is where the msater takes all of its notes.  This is how the master can fail and the cluster can still recover.

    And, yes, this needs to be its own volume / LUN - but it does not need to be very large.

     


    Brian Ehlert (hopefully you have found this useful)
    Wednesday, May 19, 2010 3:16 PM
    Moderator
  • Guys,

    Very related question:

    Which Quorum configuration should it be then?

    Does it mean: No Majority: Disk Only (not recommended)

    Does the answer remain the same for 2/3/4 nodes clusters?

    • Node Majority (recommended for clusters with an odd number of nodes)

      Can sustain failures of half the nodes (rounding up) minus one. For example, a seven node cluster can sustain three node failures.
    • Node and Disk Majority (recommended for clusters with an even number of nodes)

      Can sustain failures of half the nodes (rounding up) if the disk witness remains online. For example, a six node cluster in which the disk witness is online could sustain three node failures.

      Can sustain failures of half the nodes (rounding up) minus one if the disk witness goes offline or fails. For example, a six node cluster with a failed disk witness could sustain two (3-1=2) node failures.
    • Node and File Share Majority (for clusters with special configurations)

      Works in a similar way to Node and Disk Majority, but instead of a disk witness, this cluster uses a file share witness.

      Note that if you use Node and File Share Majority, at least one of the available cluster nodes must contain a current copy of the cluster configuration before you can start the cluster. Otherwise, you must force the starting of the cluster through a particular node. For more information, see "Additional considerations" in
      Start or Stop the Cluster Service on a Cluster Node.
    • No Majority: Disk Only (not recommended)

      Can sustain failures of all nodes except one (if the disk is online). However, this configuration is not recommended because the disk might be a single point of failure.
    Wednesday, May 19, 2010 8:42 PM

All replies

  • Hi Mark,

    You will always need a quorum disk because this is the cluster’s configuration database.

    We can say that the quorum has two very important jobs:

    • First of all, it tells the cluster which node should be active. The quorum tells the cluster which node is currently active
      and which node or nodes are in stand by.
    • Second of all, the quorum intervenes when communications fail between nodes.

     

    So the response is yes Mark ... :)

    Hope to help you.


    David LACHARI
    Wednesday, May 19, 2010 2:12 PM
  • As David states, a cluster always needs some type of quorum.

    The quorum is the recording system of a cluster - it is how the cluster knows what is happening, what is in process, etc.  It is where the msater takes all of its notes.  This is how the master can fail and the cluster can still recover.

    And, yes, this needs to be its own volume / LUN - but it does not need to be very large.

     


    Brian Ehlert (hopefully you have found this useful)
    Wednesday, May 19, 2010 3:16 PM
    Moderator
  • Hi,

    Just to add to the allready good answers...

    The Quorum dosn't allways need to be a disk - quorum can be achieved by node majority too - that is, if you have an uneven number of nodes, you don't need a quorum disk. With an even number of nodes (like in you case), you need a quorun disk.

    /Lars Hulbæk

    Wednesday, May 19, 2010 5:46 PM
  • Guys,

    Very related question:

    Which Quorum configuration should it be then?

    Does it mean: No Majority: Disk Only (not recommended)

    Does the answer remain the same for 2/3/4 nodes clusters?

    • Node Majority (recommended for clusters with an odd number of nodes)

      Can sustain failures of half the nodes (rounding up) minus one. For example, a seven node cluster can sustain three node failures.
    • Node and Disk Majority (recommended for clusters with an even number of nodes)

      Can sustain failures of half the nodes (rounding up) if the disk witness remains online. For example, a six node cluster in which the disk witness is online could sustain three node failures.

      Can sustain failures of half the nodes (rounding up) minus one if the disk witness goes offline or fails. For example, a six node cluster with a failed disk witness could sustain two (3-1=2) node failures.
    • Node and File Share Majority (for clusters with special configurations)

      Works in a similar way to Node and Disk Majority, but instead of a disk witness, this cluster uses a file share witness.

      Note that if you use Node and File Share Majority, at least one of the available cluster nodes must contain a current copy of the cluster configuration before you can start the cluster. Otherwise, you must force the starting of the cluster through a particular node. For more information, see "Additional considerations" in
      Start or Stop the Cluster Service on a Cluster Node.
    • No Majority: Disk Only (not recommended)

      Can sustain failures of all nodes except one (if the disk is online). However, this configuration is not recommended because the disk might be a single point of failure.
    Wednesday, May 19, 2010 8:42 PM
  • Hi,

    Just to add to the allready good answers...

    The Quorum dosn't allways need to be a disk - quorum can be achieved by node majority too - that is, if you have an uneven number of nodes, you don't need a quorum disk. With an even number of nodes (like in you case), you need a quorun disk.

    /Lars Hulbæk

    Lars,

    >if you have an uneven number of nodes, you don't need a quorum disk.

    But without quorum resource, 3 nodes cluster can withstand one node failure only…

    If two nodes go down for whatever reason - the last one will bring down all clustered resources…

    IMO, that’s definitely not what most people want…


    Wednesday, May 19, 2010 8:49 PM