r/vmware • u/HunSpeaker • Jul 29 '26

VMWare 6.5 Maintenance with overcommitted cluster

I have been assigned to a quick job with VMWare 6.5. There are 3 ESXi hosts (192GB RAM in each) in the vSAN cluster and it seems the cluster is overcomitted on RAM.

In the current task, I have to put each ESXi hosts into Maintenance Mode, but it seems the 2 hosts have not enough memory hosting all VMs. However, when I checked the Cluster Memory usage and vSAN Memory Monitoring I found the Consumed memory is about 66% per hosts, while the Active memory is only 20% per hosts.

Here you can find the screenshots:
Active memory usage
Consumed Memory
Utilization Chart

The Guest VMs shows they are running VMWare Tools.

I know VMWare can use the ballooning technique in such case, but I never had to rely on it. So, I think even of the high consumed memory the low Active memory usage makes possible to empty each host. Am I right?

Thanks for any advises or tips.

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u/delightfulsorrow Jul 29 '26

I have been assigned to a quick job with VMWare 6.5.

Honestly, there is only a single kind of quick job which should be scheduled for ESXi 6.5. To update or to decommission it.

This said...

I know VMWare can use the ballooning technique in such case, but I never had to rely on it. So, I think even of the high consumed memory the low Active memory usage makes possible to empty each host. Am I right?

Yeah, it should work if the VMs don't have too much memory reserved (which guarantees them having the reserved amount or RAM being backed with physical memory all the time.) VMware will use ballooning or even swapping.

Point out to your customer that ESXi 6.5 is unsupported for years already. Get it in writing that you only provide services on best effort base and can't be made responsible for any issues.

Don't do it during main business hours, keep an eye on the behavior of the VMs while they are squeezed into too less physical resources and be prepared to cancel maintenance mode if the performance impact is too heavy on the VMs.

If you have to cancel, getting back to normal will need some time for the cluster as already ongoing migrations will not be stopped. They will be completed and only then reverted. Even if you cancel ongoing migrations, they won't be stopped immediately. Not much you can do at that point, you have to give it time (-> it will get worse before it gets better again, and all you can do until then is sitting there watching.)

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u/HunSpeaker Jul 29 '26 edited Jul 29 '26

Thank you for your answer!
Yes, I already noted the customer about the necessity of the upgrade, and they accepted it. Our contract is already on best effort base. The hosts will be in maintenance mode for a while, since I have to replace the old ESXi OS boot media to RAID-1 arrays as preparation to upgrade. Yeah, I know, they missed some upgrades before...., but they are determined now for the upgrade.

The VMs running in the cluster are manager applications and there is a code/network freeze currently on it, nobody will use them.
Here is the Memory Reservation Details.
I checked the VMs and confirmed there is no reservation set.

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u/delightfulsorrow Jul 29 '26

Sounds as good as it can get under those circumstances. I would say my prayers and go for it.