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vSAN Health Service - Cluster health - vSAN disk balance (2144278)

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This article explains the Cluster Health - vSAN Disk Balance check in the vSAN Health Service and provide details on why it might report an error.


Q: What does the Cluster Health - vSAN Disk Balance check do?

A: Every disk in an ESXi host has a total capacity, and also the percentage of used space. Currently we use (actual physical disk usage)/(physical disk capacity) as the disk usage.
vSAN system attempts to balance the load balance between disks in the vSAN cluster, but at any given moment the load per disk varies.
The vSAN disk balance test checks each healthy disk in the vSAN cluster, and gets a summary of the average disk usage, maximum disk usage, average load variance, and maximum load variance.
If some of the disk's load variance exceeds the threshold, the load balance is not in properly achieved, and another tab shows the detailed information for these disks, including the percentage exceeding the threshold and data which should be moved to bring the variance below the threshold.

Q: What does it mean when it is in an error state?

A: If this check is yellow, it means that the disk load variance between some disks exceeded the threshold at some point in time.
The threshold is set at 30. So if disk A's usage is 45% and disk B's usage is 10%, the load variance between disk A and disk B is 35, which exceeds the threshold.

For more information about this issue, refer to the following article: "Virtual SAN Disk Balance" warning alarm during vSAN health check (2148484).

Q: How does one troubleshoot and fix the error state?

A: vSAN will reactively load balance the cluster. But you can trigger a proactive rebalance by clicking the Rebalance Disks button, if it is available.
When you click the Rebalance Disks button, vSAN begins to execute the rebalancing process.
If proactive rebalancing is in process, you can click the Stop Rebalance button to stop the rebalancing process.


vSAN disk balance

See Also

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