Fault Tolerance Issue

[MuchB]

Hello guys!

I recently setup fault tolerance on my vcenter 6.7 and it was working perfectly. But now, if the VM with fault tolerance enabled is running on my primary esxi host and i turn the primary esxi host off, the vm goes to my secondary esxi host with 0 disruption and works perfectly fine. But when I power back on my primary esxi host and let it power up and turn off my secondary esxi host, it seems like the vm restarts or powers off.

So when i login to the windows vm, everything is closed and now how it was left.

Any help would be greatly appreciated.

Thank you!

[sk84]

How long are you gonna wait to shut down the second host? FT does not jump back to the primary VM. FT doesn't work that way.

If there is a failover to the secondary VM, vSphere makes it primary and tries to create a new shadow VM at the same time. But if you only have 2 hosts and one is offline, this can't happen, because primary and secondary VM must not exist on the same host. And creating the new secondary VM will take some time, depending on the size of the VM.

[MuchB]

I was waiting a few minutes before shutting down esxi host #2 - basically when the vms turned back on in the esxi host #1.

I have a shared datastore on a separate server (off of the esxi hosts) and I have migrated the VM's storage to it (the one with fault tolerance enabled). Does that help my situation at all? Or do I need 3 esxi hosts to make it work the way I described in the opening post? Or am I just not waiting long enough? I feel like it was doing what I described in the opening post the first few times.

Thanks for your help, I am understanding it better.

[sk84 · Accepted solution]

A shared storage is not necessary for FT and does not help you in this situation. The only requirement that must be met at this point is that all hosts on which an FT VM can be placed must be in a cluster with HA & FT enabled. And as soon as Primary and Secondary VM do not see each other anymore, the Secondary VM becomes active and becomes the new Primary VM and vSphere creates a new Secondary VM with an identical copy of the new Primary VM. In this way, split-brain situations are avoided.

You can check the FT status by checking the "vSphere Fault Tolerance" area in the Summary tab of the FT VMs. There you can see the status, e.g. "Protected" or "Unprotected" and also which VM is the Primary and Secondary.

[MuchB]

Thank you kindly!