Why doesn't VMWare DRS automatically migrate VMs when a host is put in maintenance mode?

Question

We have 4 ESXi 5.0 hosts in a VMWare cluster on shared storage (NFS) with DRS and HA on.

We want to perform a memory upgrade on one of the hosts. We put that host in maintenance mode but DRS did not automatically live migrate the VMs.

I'm thinking it has something to do with our settings:

I'm admittedly not that familiar with with VMWare's DRS. Can someone offer us some guidance on this?

Solution

This should work, but there's more about your environment that we'd need to know. Your issue is most likely tied to the Admission Control settings for your 4-host cluster. The specifics of how to configure Admission Control properly is outside the scope of this question, though.

Can you try disabling HA Admission control and attempting the Maintenance Mode on the host again?

Comments

[ewwhite]

We may need more information. Did any VMs move?

[NukaRakuForgotEmail]

None of the VMs moved.

[NukaRakuForgotEmail]

That did it. I think I kind of understand why. Basically: If we go down to 3 hosts, we won't have enough for a 1 host failure. Is that it in a nutshell?

[ewwhite]

On the surface, yes... but the Admission Control doesn't mean what people think it means. It's pretty useless for the scale of your cluster unless you're using reservation pool or reservations at the VM-level.