Maintenance mode prevents all VMs from being powered on that host. If there are any running VMs, the host cannot go into maintenance mode until the VMs are powered off.
It is useful in preventing additional VMs from being powered on. The mode is needed if you are upgrading the host, or removing the host from a cluster.
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One other cool thing... If the host is using DRS and you put the host into maintenance mode, it will DRS all of the running VMs off to other hosts. Very cool to see.
mind you, it still has the same dependencies and limitations of VMotion in that if you, for some reason, leave a CD or Floppy attached to a running VM it won't go across and "maintenance mode" won't complete.
moral of this story; always disconnect your CD and Floppy when not in use....
That is, unless your virtual CD or floppy is mapped to a file that is in a shared datastore.
Haven't tried that yet on VI3. Nice.
Can be prevented from completing by defining some rules at the cluster level that will prevent certain co-existance models to occur. In other words you need to be aware of possible conflists with rules (e.g. two guests not allowed to co-exist on the same host) and manually power down/shift the guests to allow maintenance mode task to complete. Otherwise it just sits there as an incomplete task with no notification.
One other cool thing... If the host is using DRS and
you put the host into maintenance mode, it will DRS
all of the running VMs off to other hosts. Very cool
Really? I thought all VM's on a host had to be shut off before you could go into Maintenance Mode? If the VM is shut off, why would DRS Vmotion it?
The only reason I say this is because we recently had an issue. We had a scheduled power outage. I powered down VM's. I put the server into Maintenance Mode. Then, I shut down the host server. When we powered back on, some of the hosts came up in maintenance mode and some didn't. To further complicate things, one of our hosts died. Linux was messed up. I was unable to vmotion any of the VM's off that host. I'm not sure if it's because I put it into Maint mode before I shut it down or not. But, I would think that as soon as I took the other DRS / HA host out of main mode, the VM's would vmotion over. They didn't. They're stuck on the dead host.