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    Ping-Node – explained.

    We wanted to provide you an in-depth explanation of the Ping-Node offering clarifications on its function and usage.

    Incorrect Ping-Node configuration and functionality can cause problems with HA clusters.

    The importance of this post is critical for a proper setup with the iSCSI Failover.

    Why do we need a ping-node or rather ping-nodes?

    DSS V6 iSCSI Failover (and soon NFS Failover) uses a heartbeat to check the Primary and Secondary hosts to each other.

    We require at least 2 NICs configured for the heartbeat. Additionally we strongly recommend using a direct crossover or what is called a point-to-point connection for the
    Volume Replication. This path must be enabled for the heartbeat as well. With a direct connection both hosts can communicate even during a switch failure and you save on 2 switch ports.

    So, what would happen if both the Primary and Secondary hosts are functioning well and are able to communicate to each other (i.e. via mentioned direct connection) but the storage client has lost network connection to the Primary host?

    For example the switch port or NIC in that path has a problem.

    The heartbeat will NOT decide about the failover procedures because both hosts “think” are OK, but still the storage client cannot access the storage. This is where the Ping Node comes into play and prevents such situations. The cluster manager realizes that the Primary host has lost access to the Ping-Node(s) but the Secondary host has access. So the cluster manager executes failover. Because of lost access to a single Ping Node will cause a failover, so it is strongly recommended to use at least 2 Ping-Nodes for every network segment which will need a Ping-Node. This will minimize failover events in case of an unreliable Ping-Node.

    Now, which network segment will need the Ping-Node(s) for monitoring? For sure not ever NIC but only those network paths which are connected to storage clients need to be monitored with Ping-Node(s).

    The best explanation can be outlined below with examples. So let’s consider the first example with bonding.

    Failover with Bonding – Click Here

    Here the storage clients (VMware, XenServer, Windows) will be connected via a bonding network segment so the Ping-Nodes are in the subnet 192.168.1.x. So a minimum of one PingNode is required, but we recommend at least 2.

    Failover with Mpio – Click Here

    In this case storage clients will be connected via both network segment paths, so Ping-Nodes are in subnet 192.168.1.x and 192.168.2.x

    So a minimum of two ping-nodes are required, but we recommend at least 4 due to the Multipath.

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    • Sarah Gin

      September 19, 09 2011 06:26:32

      I want to ping a server from my node.js app. Is it possible??

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      • Janusz Bak

        February 03, 02 2012 07:59:04

        YES! Using your storage client as the ping node is a VERY GODD idea. Please read my comment to the next question.

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    • pme

      February 02, 02 2012 12:36:31

      In the Graphic for multipath the Ping Nodes are in the 192.168.1 and 192.168.2 Networks, but the text here says they ought to be in subnet 192.168.10.x and 192.168.20.x.
      Which is correct or are both ok?
      Would it not make sense to use the Storage Clients as the ping nodes as effectively they are the machines that need access?

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      • Janusz Bak

        February 03, 02 2012 07:57:25

        Ping nodes are in the same subnet as physical IP of NICs used for storage access.
        Using your storage client as the ping node is a VERY GODD idea. We promote it in our webinars and in how-to documents.
        In case of ESXi you can just add vmkernel and set an IP in the same subnet as physical IP of the storage NIC.
        In case of XEN or Windows you can add extra IP, next to the main IP.

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    • Rainer

      May 02, 05 2012 08:52:29

      In your blog example for MPIO its recommended that the ping nodes are in the same subnet (192.168.10.x, 192.168.20.x) like the virtual ip addresses used on open e servers.

      I see a problem in this setup: The virtual ip addresses on open-e hosts are only available when failover is already up and running. But to get failover up and running you need to have a working ping node, that in this setup needs to be able to ping a host that is in the subnet of the virtual ip address which in turn is only possible when failover is activated.

      So this very setup shoots itself in its foot, doesn’t it?


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      • Janusz Bak

        May 07, 05 2012 07:34:23

        You are absolutely right. It was mistake in the blog.
        I have fixed it already.
        It must be subnet 192.168.1.x and 192.168.2.x, not
        192.168.10.x and 192.168.20.x.
        Thank you very much!!!

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