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Understanding Quorum Disk RRS feed

  • Question

  • We've got a simple 3-node Hyper-V cluster setup which initially passed the verify tool 100%.  We created it, added the drives from the SAN, everything works great (including planned/unplanned fail-overs) BUT.... when we now re-verify the cluster we get a quorum warning.

    I understand that we can designate one of the disks on the SAN as a quorum disk, and if we do that warning goes away, but if we do that does that mean we cannot use that disk for actual storage of VMs?

    • Edited by B-Flo Friday, March 14, 2014 7:15 PM
    • Moved by BrianEhMVP Friday, March 14, 2014 7:25 PM
    Friday, March 14, 2014 7:04 PM

Answers

  • The cluster has the logic built in so that it knows with a three node cluster a file share or disk witness is not needed to establish quorum in case of a node failure.  However, if you had created a two node cluster, it would have automatically grabbed one of the disks to use as a disk witness.  A disk witness cannot be used for any other purpose.  It cannot be a data disk. If you want to put a disk witness into the cluster, you should create a volume with just 512 MB to 1 GB of storage, add it to the cluster, and change the cluster quorum to disk witness, ensuring that disk is assigned as the witness disk.

    If you want to learn more about how the quorum works in a cluster, search TechNet for 'understanding failover cluster quorum' and you will find some informative articles.


    .:|:.:|:. tim

    Saturday, March 15, 2014 9:37 PM
  • We've got a simple 3-node Hyper-V cluster setup which initially passed the verify tool 100%.  We created it, added the drives from the SAN, everything works great (including planned/unplanned fail-overs) BUT.... when we now re-verify the cluster we get a quorum warning.

    I understand that we can designate one of the disks on the SAN as a quorum disk, and if we do that warning goes away, but if we do that does that mean we cannot use that disk for actual storage of VMs?

    With a 3 node cluster you can use "node majority" so everything should work fine w/o Quorum disk.

    Right, you don't store any data on Quorum disk. Keep it for system (cluster voting) use. 

    For your reference see:

    Understanding Quorum

    http://technet.microsoft.com/en-us/library/cc731739.aspx

    Hope this helped a bit :)


    StarWind VSAN [Virtual SAN] clusters Hyper-V without SAS, Fibre Channel, SMB 3.0 or iSCSI, uses Ethernet to mirror internally mounted SATA disks between hosts.

    • Proposed as answer by BrianEhMVP Friday, March 14, 2014 7:25 PM
    • Marked as answer by Alex LvModerator Monday, March 24, 2014 10:59 AM
    Friday, March 14, 2014 7:22 PM
  • Generally speaking, it is recommended to always configure a Witness.  The Witness can be either a Disk or a File Share.  If you have shared storage, then a Disk is recommended.  This should be a dedicated LUN, and as Tim said you can create a small LUN for the Disk Witness. In this doc you will find the recommendations for the Disk Witness:
    http://technet.microsoft.com/en-us/library/cc770620(v=WS.10).aspx

    It is true that a 3-node cluster can function properly without a Witness configured.  But with a Witness the cluster will behave better if you have multiple node failures.  So let's say you have a node failures and get down to 2-nodes in the cluster.  In the case of 2-nodes in cluster membership, it's best to have a Witness to ensure the cluster survives if you have an additional unexpected failure of a node.  It just helps the cluster be as resilient as it can be...

    Thanks!
    Elden

    Sunday, March 16, 2014 1:41 PM
    Owner

All replies

  • We've got a simple 3-node Hyper-V cluster setup which initially passed the verify tool 100%.  We created it, added the drives from the SAN, everything works great (including planned/unplanned fail-overs) BUT.... when we now re-verify the cluster we get a quorum warning.

    I understand that we can designate one of the disks on the SAN as a quorum disk, and if we do that warning goes away, but if we do that does that mean we cannot use that disk for actual storage of VMs?

    With a 3 node cluster you can use "node majority" so everything should work fine w/o Quorum disk.

    Right, you don't store any data on Quorum disk. Keep it for system (cluster voting) use. 

    For your reference see:

    Understanding Quorum

    http://technet.microsoft.com/en-us/library/cc731739.aspx

    Hope this helped a bit :)


    StarWind VSAN [Virtual SAN] clusters Hyper-V without SAS, Fibre Channel, SMB 3.0 or iSCSI, uses Ethernet to mirror internally mounted SATA disks between hosts.

    • Proposed as answer by BrianEhMVP Friday, March 14, 2014 7:25 PM
    • Marked as answer by Alex LvModerator Monday, March 24, 2014 10:59 AM
    Friday, March 14, 2014 7:22 PM
  • With a 3 node cluster you can use "node majority" so everything should work fine w/o Quorum disk.

    Thanks so much for your help.

    Forgive my ignorance, but in this context do we already have "node majority" by virtue of creating the 3-node cluster (without quorum disk) or is that something I need to pro-actively configure?

    Friday, March 14, 2014 7:30 PM
  • The cluster has the logic built in so that it knows with a three node cluster a file share or disk witness is not needed to establish quorum in case of a node failure.  However, if you had created a two node cluster, it would have automatically grabbed one of the disks to use as a disk witness.  A disk witness cannot be used for any other purpose.  It cannot be a data disk. If you want to put a disk witness into the cluster, you should create a volume with just 512 MB to 1 GB of storage, add it to the cluster, and change the cluster quorum to disk witness, ensuring that disk is assigned as the witness disk.

    If you want to learn more about how the quorum works in a cluster, search TechNet for 'understanding failover cluster quorum' and you will find some informative articles.


    .:|:.:|:. tim

    Saturday, March 15, 2014 9:37 PM
  • Generally speaking, it is recommended to always configure a Witness.  The Witness can be either a Disk or a File Share.  If you have shared storage, then a Disk is recommended.  This should be a dedicated LUN, and as Tim said you can create a small LUN for the Disk Witness. In this doc you will find the recommendations for the Disk Witness:
    http://technet.microsoft.com/en-us/library/cc770620(v=WS.10).aspx

    It is true that a 3-node cluster can function properly without a Witness configured.  But with a Witness the cluster will behave better if you have multiple node failures.  So let's say you have a node failures and get down to 2-nodes in the cluster.  In the case of 2-nodes in cluster membership, it's best to have a Witness to ensure the cluster survives if you have an additional unexpected failure of a node.  It just helps the cluster be as resilient as it can be...

    Thanks!
    Elden

    Sunday, March 16, 2014 1:41 PM
    Owner
  • Thanks very much everyone.  It didnt dawn on me at first that the quorum disk could be a partition (as oppose to an actual physical disk in the SAN, which would of course be very wasteful <g>).

    I just took a 1GB slice from one of the vdiscs, configured it as the quorum disk, and done-deal (more or less for "free").

    Monday, March 17, 2014 2:07 PM
  • No!  Please do not do that.  Yes, it can be done, but it is absolutely not what you want.  The volume, not the partition, is the shared resource.  So by making the witness disk a partition on an existing volume, you have just tied the cluster group to the other group that owns the volume with the partition.

    Please simply create a small LUN and dedicate it to the witness disk.  You will be much happier in the long run.


    .:|:.:|:. tim

    Monday, March 17, 2014 9:37 PM