jk_sui
Enthusiast
Enthusiast

vSAN Auto Rebalancing

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Hi guys

I have a question about vSAN (6.7) rebalancing.

In the docs it states, that in vSAN automatic rebalancing is enabled by default.

About vSAN Cluster Rebalancing

But in all my clusters the advanced option "automatic rebalancing" is disabeld (by default).

One of my clusters had a "vSAN Disk balance" warning in the health check, which did not clear itself.

I activated the "automatic rebalancing" and it started to rebalance right away and the warning got cleared.

Does vSAN really rebalance automatically or do i have to enable "automatic rebalancing" on every cluster?

Thanks for any help from the community!

Cheers

Jonas

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TheBobkin
VMware Employee
VMware Employee

Hello Jonas,

The documentation you referenced is referring to 'Reactive Rebalance' as opposed to 'Proactive Rebalance' - the former starts moving data automatically when the CLOM rebalance threshold has been reached on any disk (80% by default).

However, this differs from 'Proactive Rebalance' which can be automated as of 6.7 U3 but still needs to be enabled on each cluster:

Configure Automatic Rebalance

Bob

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TheBobkin
VMware Employee
VMware Employee

Hello Jonas,

The documentation you referenced is referring to 'Reactive Rebalance' as opposed to 'Proactive Rebalance' - the former starts moving data automatically when the CLOM rebalance threshold has been reached on any disk (80% by default).

However, this differs from 'Proactive Rebalance' which can be automated as of 6.7 U3 but still needs to be enabled on each cluster:

Configure Automatic Rebalance

Bob

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GreatWhiteTec
VMware Employee
VMware Employee

Hi jk_sui,

There are a few approaches to rebalance.

1- Reactive Rebalance - Happens when a device reaches 80% (default) of capacity, vSAN will try to rebalance the load more evenly across the cluster.

2- Proactive Rebalance - Already in place prior to 6.7U3, vSAN detects variance between devices and alerts you on it. It will be your responsibility to rebalance it manually.

3- Automatic Rebalance - New in 6.7U3 - Detects the variance, alerts, and auto remediates itself. Desired state is to keep alert green and data rebalanced as much as possible. There is quite a bit more behind the scenes...

There are quite a few improvements in 6.7 U3 when it comes to rebalancing, rebuilding, prioritization, etc. See tech review for more info.

vSAN_6.7_U3_Technical_Overview

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jk_sui
Enthusiast
Enthusiast

Thanks GreatWhiteTec​!

I understand it now.

Can you tell me where I can manually rebalance? As per your second bulletpoint?

I couldn't find it anywhere.

Thanks again and regards

Jonas

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jk_sui
Enthusiast
Enthusiast

Thanks TheBobkin​ for the quick response.

Very much appreciated!!

Jonas

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TheBobkin
VMware Employee
VMware Employee

jk_sui, Proactive Rebalance (if needed) can be started from the Health check associated with it:

Cluster > Monitor > vSAN > Health > vSAN disk balance > Rebalance Disks

VMware Knowledge Base

or via RVC:

https://www.virten.net/2017/05/vsan-6-6-rvc-guide-part-2-cluster-administration/#vsan-proactive_reba...

If it is a 6.7 U3 or later cluster then this can be enabled/disabled to be automatic via the steps I linked in my first comment.

Bob

jk_sui
Enthusiast
Enthusiast

Maybe I am blind, but i just don't see a manual rebalancing option there.

Please see screenshots attached.


Thanks Jonas

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TheBobkin
VMware Employee
VMware Employee

jk_sui Yes, because it has already been started as it shows in your second screenshot.

Another place you can see this is via RVC:

https://www.virten.net/2017/05/vsan-6-6-rvc-guide-part-2-cluster-administration/#vsan-proactive_reba...

Bob

jk_sui
Enthusiast
Enthusiast

Thanks TheBobkin​ for your help!

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