Forum Discussion

linuly's avatar
linuly
Level 4
6 years ago

vcs node

hi

i like to clarify.

when a node join to vcs then in its memory all the information from the other nodes are filled.thus this node sees if there he should bring up the resource group that normally start on it.when he leave the cluster the information is updated on remaining cluster nodes and the service group fail over.right?

tnx

  • frankgfan's avatar
    frankgfan
    6 years ago

    Hello,

    In CVM configuration, any vx* commands which will lead to a vxvm configuration change (commjands like vxassist, vxmake, vxsd, vxplex etc) need to be executed on the CVM master (with new releases from 6.2, the command can be issued on any nodes as now there is a GAB port y which can ship commands to the cvm master for execution).

    VCS commands like hares, hagrp, haclus etc do not change VxVM metadata so can be executed on any nodes in the cluster, so long as the node is in online running state in the cluster.

    Frank

  • RiaanBadenhorst's avatar
    RiaanBadenhorst
    Level 6
    6 years ago
    It works like this.

    There is a special network between the cluster nodes which is called llt. This network allows another protocol called gab to keep all cluster nodes up to date with the status of all cluster resources. Any status changes and configuration updates are distributed via gab.

    When a node starts up it joins network and check if anybody else is online. If there are enough nodes online it gets the configuration from them and decides based on the rules in the main.cf if it needs to online anything (based on the current state in cluster).

    If it finds that nobody is online it has to wait for enough nodes to join it. When they do, it distributes the configuration to the others and then again based on the rules, they online the resources.

    For nodes leaving, or resources failing, the state is again distributed to all nodes and based on the rules in the configuration they decide where to online resources

    Thats it at a high level
  • frankgfan's avatar
    frankgfan
    Moderator
    6 years ago

    Hello,

     

    when a node starts and if there is another node in running state, the node will take a snapshot of cvs configuration from the running node via llt network.  you can see this info from engine_A.log.  if there is not any node in running state, the node will read on disk vcs configuation (main,cf) and buid up the cluster.

     

    if a node is shutdown, hastop command will be executed as part of system shutdown,  since a system shutdown is considered as a system admin action, not a true failure., vcs service groups may not be switched over.

     

    here are some hastop command options and their meanings:

        The -local option stops the VCS server on the system on which the command is issued. When the VCS server stops a system, the system’s service groups are also stopped.

       The -force option stops the VCS server, but allows the service groups to continue running.

       The -evacuate option migrates all groups to other systems, if possible.

       The -noautodisable option ensures that service groups that can run on the node for which hastop is invoked are not autodisabled while VCS is stopped. The -noautodisable option can also be used with -evacuate option, but not with -force option.

    please also read this technote https://support.symantec.com/en_US/article.TECH11477.htm to know some vcs behavior in a system restart.

    Frank

     

    • linuly's avatar
      linuly
      Level 4
      6 years ago

      Hi,

      In vcs cluster an designated coordinator is elected.When the cluster is running every hagrp,hares including resource switch  so on command will talk to DC.right?

      tnx

       

      • frankgfan's avatar
        frankgfan
        Moderator
        6 years ago

        Hello,

        there are two types VCS configurations:  failover and CVM (cluster volume manager, also known as parallel configuration).  In CVM configuration there is one node elected as a CVM master.

        In failover configuration (a service group is onlined on one node at any given time) there is no master node.

        Can you please elaberate the followings?

        1. an designated coordinator 

        2. DC

        is your cluster running on Windows platform or Unix?

        Frank

  • CliffordB's avatar
    CliffordB
    Level 4
    6 years ago

    There have been good answers, but I want to make a few clarifications:

    In VCS (outside of cluster file system), there is no "master" node.  All servers that participate in the cluster have identical state status for all resources.  All VCS commands are atomic.  Either all servers get updated successfully, or the command falis.  VCS is a state machine that works across mulitple separate operating system instances.   Each OS has a complete picture of the state of all servers participating in the cluster.  

    As host enter and exit the cluster, all active nodes are updated.  Every time a resoruce or service group is changed: turned on or off or moves, created or deleted, all nodes are notified.  Again, either all nodes are updated, or the change fails.

     

    Regarding behavior of ServiceGroups when a node joins or leaves the cluster:  the behavior is dictated by several paramenters.  As a default, when a node fails, its ServiceGroups are moved to other existing cluster members.  How the ServiceGroups are distributed is beyond this discussion.  The Admin guide give very detailed examples on how to control behavior of ServiceGroups when a node leaves on purpose (admin shutsdown a server for maintenance) versus a hardware/softawre failure.

    Cluster Volume Manager does have a master/slave system for lock managment only.  If you are not using CFS, then you don't need to consider the idea of master/slave.

    • linuly's avatar
      linuly
      Level 4
      6 years ago

      hi,

      Tnx Frankgfan and Riaan.I posed this question on Saturday.I have not expected somebody to reply on weekend.The people were very kind and replied me straightaway and very in depth.

      You Clifford just shows me how much you are uneducated  arrogant and so on.It were better if you abstained to reply.Guys like you i met very often.You can not understand to be polite.

      "My customers spend the weekends at home with family, not in the datacenter."