0

vSAN Proactive Rebalance

One great feature of vSAN is that it will try to reactivley rebalance itself in situations where the disk load variance between disks exceeded the 30% threshold . The vSAN disk balance test checks each healthy disk in the vSAN cluster and will get a summary of the average disk usage, maximum disk usage, average load variance, and maximum load variance.

As mentioned above the threshold is set at 30% so for example, if a disk usage is at 55% and another disk  usage is 10%, the load variance between the two disks is 45%, which exceeds the threshold. Rebalance is therefore needed.

In summary, the whole point of vSAN rebalance is to make sure that your disks are used efficiently

Why are my disks not balanced?

Typically, disks get unbalanced when you put your hosts into maintenance mode and the option of evacuated data from them is chosen.

Adding new disks or disk groups  to your hosts and even  introducing a new node to the cluster  will also introduce an unbalance as vSAN will always try to consume these newly introduced disks as soon as possible.

How do I check if my disks are balanced?

Checking your disk balance status can be done via the GUI or via command line.

In your vSphere client, click on your cluster > Monitor > vSAN > Health > Under the cluster test > vSAN Disk Balance

To check via the command line:

  1. Log into the Ruby vSphere Console.
  2. Change to the computers namespace.
  3. To see how much data needs to be rebalanced, Run this command on your vSAN cluster

/localhost/cluster> vsan.proactive_rebalance_info

Max usage difference triggering rebalancing: 30.00%
Average disk usage: 44.00%
Maximum disk usage: 54.00% (16.00% above minimum disk usage)
Imbalance index: 6.00%
No disk detected to be rebalanced

How do I initiates a manual rebalance?

Running a manual rebalance can be down via the GUI or via command line.

In your vSphere client, click on your cluster > Monitor > vSAN > Health > Under the cluster test > vSAN Disk Balance

To check via the command line:

  1. Log into the Ruby vSphere Console.
  2. Change to the computers namespace.

To start the rebalance
/localhost/cluster>  vsan.proactive_rebalance -s mycluster

To Monitor the status of the rebalance
/localhost/cluster> vsan.proactive_rebalance_info mycluster

Resync Throttling

If your rebalance trigger high network load that affects the stability of the cluster,  you can enable Resync Throttling (vSAN 6.6 Feature)  which allows you to have control over how much bandwidth these operations take. Please note: VMware recommends that the throttling should only be changed in extreme scenarios.

In your vSphere client, click on your cluster > Monitor > vSAN >Resyncing Components

I hope this post was helpful. Be social share.

How useful was this post?

Click on a star to rate it!

Average rating / 5. Vote count:

Sharing is caring!

Related Post

Leave a Reply

Your email address will not be published. Required fields are marked *