Thursday, 26 December 2019

vSAN 6.x Cluster Rebalancing

vSAN Cluster rebalancing evenly distributes resources across the cluster to maintain consistent performance and availability.

If you remove capacity devices from the vSAN cluster, the disk groups might become unbalanced. If you add hosts or capacity devices to the vSAN cluster, the disk groups might become unbalanced. Rebalancing also occurs when you place a vSAN host in maintenance mode.

vSAN Cluster rebalancing is done using two methods.
  • Automatic Rebalance 
  • Manual Rebalance 
Automatic Rebalance:

When any capacity device in your cluster reaches 80 percent full, vSAN automatically rebalances the cluster.

Run the following RVC commands to monitor the rebalance operation in the cluster:
  • vsan.check_limits
Verifies whether the disk space use is balanced in the cluster.
  • vsan.whatif_host_failures
Analyzes the current capacity use per host, interprets whether a single host failure can force the cluster to run out of space for reprotection, and analyzes how a host failure might impact cluster capacity, cache reservation, and cluster components. The physical capacity use shown as the command output is the average use of all devices in the vSAN cluster.
  • vsan.resync_dashboard
Monitors any rebuild tasks in the cluster.


Manual Rebalance:

You can manually rebalance through the cluster health check, or by using RVC commands.

If the vSAN disk balance health check fails, you can initiate a manual rebalance. Under Cluster health, access the vSAN Disk Balance health check, and click the Rebalance Disks button.

Use the following RVC commands to manually rebalance the cluster:

vsan.check_limits - Verifies whether any capacity device in the vSAN cluster is approaching the 80 percent threshold limit.

vsan.health.cluster_rebalance <cluster> - Manually starts the rebalance operation. When you run the command, vSAN scans the cluster for the current distribution of components, and begins to balance the distribution of components in the cluster. Use the command options to specify how long to run the rebalance operation in the cluster, and how much data to move each hour for each vSAN host. For more information about the command options for managing the rebalance operation in the vSAN cluster, see the RVC Command Reference Guide.

Note:

When you manually rebalance the disks, the operation runs for the selected time period, until no more data needs to be moved. The default time period is 24 hours. If no data is being moved, vSAN ends the rebalancing task.

Using Web/vSphere clients 

Navigate to the vSAN cluster.
Click the Monitor tab.

vSphere Client:
  • Under vSAN, select Health. 
  • Expand the Cluster health category, and select vSAN Disk Balance. You can review the disk balance of the hosts. 
  • In the vSAN Disk Balance page, click Disk Balance. 

vSphere Web Client:
  • Click vSAN. 
  • Under vSAN, click Health. 
  • Expand the Cluster health category, and select vSAN Disk Balance. 
  • You can review the disk balance of the hosts. 
  • Click the Proactive Rebalance Disks button to rebalance your cluster.

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