Q. What's the difference between Redirected Access and Maintenance mode for a Cluster Shared Volume (CSV)?

A. You can place a CSV in four states, as explained here.

  • Direct Access: In this state, the CSV is available to all nodes in the cluster as part of the ClusterStorage namespace and nodes in the cluster directly access the CSV for most IO. Only metadata operations are sent to the coordinator node.

  • Redirected Access: In this state, the CSV is available to all nodes in the cluster as part of the ClusterStorage namespace, but all nodes in the cluster except the coordinator node perform their IO via the coordinator node. This IO is transported via SMB2. It should be noted that if a node loses direct connectivity to a CSV (such as a loss of iSCSI connectivity or Fibre Channel cable failure), that node will automatically switch to redirected access mode for that specific CSV so it can continue functioning. Redirected access is used in planned situations where you need to perform certain disk actions that can't have multiple nodes accessing and locking files concurrently, such as a VSS backup.

  • Maintenance mode: When you place a CSV in maintenance mode, the cluster service on each node in the cluster works out which resources are using the CSV and stops them using their configured action, such as save state or shut down. This means no resources can use the CSV. The CSV is then removed from the ClusterStorage namespace. The LUN is still online on the coordinator node for certain types of operations and can be accessed via the CSV's GUID, or you can add a mount point. You use this state to perform a Chkdsk where you need to fix sectors. When you're finished with maintenance, you need to manually start any virtual machines that were stopped.

  • Offline: When a CSV is offline, the content isn't available to any node and is no longer available under the ClusterStorage namespace.

Watch this video to learn more about Windows Server 2008 R2 clustering and virtualization

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