Cheng's Random Thoughts on System Management

Senior Program Manager, MSD

What you need to know about Maintenance Mode

What you need to know about Maintenance Mode

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Hello folks,


As you can see from the news, we’ve released our beta for SCVMM 2008 R2, which offers support to Windows Server 2008 R2 (live migration, etc.) and a bunch of exciting new features.


Today, I wanted to introduce to you our new VMM Maintenance Mode feature in VMM R2.


What is maintenance mode?

·         In Virtual Machine Manager (VMM) 2008 R2, you can start maintenance mode for a virtual machine host anytime that you need to perform maintenance tasks on the physical host, such as applying security updates or replacing hardware on the physical host computer.

·         We support start / stop maintenance mode for Hyper-V hosts, Virtual Server hosts, as well as VMWare ESX hosts.



How does it work “under the hood”?

·         To start or stop maintenance mode on a host,

o   In the VMM Administrator Console, in Hosts view, click a host, and then in the Actions pane, click either Start maintenance mode or Stop maintenance mode.

o   Or from a PowerShell window, use cmdlet “disable-VMHost” to put a host into maintenance mode, and use cmdlet “enable-VMHost” to take the host out of maintenance mode.

·         Entering maintenance mode

o   This action can be applied to all host and host clusters.

o   For Windows-based virtualization hosts

§  If they are Win7 clusters (capable of live migration), two options  would be presented on the UI:

·         The default option is to live migrate all running HA VMs, save-state all non-HA running VMs and put the host in maintenance mode.

·         The other option is to simply save-state all running VMs (no migration), and put the host in maintenance mode.

§  If they are standalone VM hosts or Win6 clusters (incapable of live migration), you would only see one option on the UI

·         Save-state of all running VMs and put the host in maintenance mode.

o   What about VMWare ESX hosts?

§  When you start maintenance mode on an ESX Server host, VMM sends an “Enter maintenance mode” request to the VMware VirtualCenter Server.

§  The system behavior of the virtual machines on the selected ESX Server host is determined by the configuration of the VMware VirtualCenter Server.

·         If the VMware Distributed Resources Scheduler is not configured, all virtual machines on the host must be either manually shut down or moved to another host to successfully start maintenance mode on an ESX Server host.

o   What about those stopped VMs?

§  We do not touch stopped VMs.

§  Even for saved-state VMs, we’re not migrating them either. They will remain on the host.

·         In maintenance mode

o   When host is in maintenance mode, here are the changes to the system behaviors on hosts:

§  Host state is not updated (the state will remain as “In Maintenance Mode” regardless of the agent status or virtualization service status);

§  No VM creation is allowed on the host;

§  No VM can be moved into this host;

§  Host is excluded from any placement (hence, self-service portal users or PRO auto-implementation won’t be able to pick this host).

o   What can users do?

§  Users actually are not blocked from most actions (except New-VM and Move-VM into this host).

§  However, please be aware that the results of the requests are all depending on the state of the host and its agent. And because the host state is no longer updated once the host is in maintenance mode, you may have a “in maintenance mode” host that is completely down but you just may not see the state change on our UI.

·         Request to remove (or force remove) the host;

·         Request to start or stop VMs on the host;

·         Request to change properties of the host;

·         Request to move VM out of the host; etc.

·         Exit maintenance mode

o   When host is taken out of maintenance mode, here is the system behavior:

§  The next host refresher will update the host state to its current state;

§  The host is now available for placement;

§  Blocks for VM creation or migration are removed from the host.

o   What about the VMs that were migrated out?

§  They are remain at their current hosts.

§  VMM does not auto-migrate-back the VMs that were migrated out.

§  Users need to evaluate and decide if there is a need to rebalance the workloads again with the resources on this host becoming available again.



Got any comments / feedbacks?

·         Give it a try by downloading our beta from here.

·         Send me your feedback.



Hope this is helpful and thanks for reading!


  • As part of VMM 2008 R2 we have added a new feature called maintenance mode. This feature enables users

  • As part of VMM 2008 R2 we have added a new feature called maintenance mode.  This feature enables

  • Is there a way to exclude a guest from being affected by putting it's host into Maintenance Mode?

    It may sound like a silly question but I have SCVMM running as a virtual machine and it resides on the local disk of one the nodes in a failover cluster.  If I put that host into Maintenance Mode, SCVMM will begine to migrate HA VM's and puts the SCVMM server into a saved state and then the whole process stops/fails becaseu SCVMM goes offline.  So I end up needing to remember that I cannot use Maintenance Mode on the one host that SCVMM lives on.

    If I could exclude this VM from the effects of Maintenance Mode then I can rely on this feature again and leave the "Automatic Stop Action" to Save so if I do shutdown the host it'll still save the VM for me anyway.

  • I should have signed in before posting that so I can get notified if/when you reply!

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