Auto-Migrate VMs During ESXi Maintenance Without Enabling DRS – Partial Migration Observed

[Mohieldin Salam]

Hello Broadcom Community,

I'm working with a vSphere environment and have a question regarding automatic VM migration when placing an ESXi host into maintenance mode.

I understand that DRS (Distributed Resource Scheduler) helps automate load balancing and vMotion across hosts, but I'd like to clarify how vCenter behaves without DRS enabled.

My Scenario:

• vCenter Server is installed and managing the cluster.
• vMotion is fully configured and tested (VMkernel ports, shared storage, etc.).
• All ESXi hosts are in the same cluster.
• DRS is currently disabled.

When I initiated "Enter Maintenance Mode" on one of the hosts, I noticed the following behavior:

Two service VMs related to vCenter Server Appliance (VCSA) migrated automatically to another host.

All other VMs remained on the host and had to be migrated manually before the host could fully enter maintenance mode.

My Questions:

• Why were only the VCSA-related machines migrated automatically, but the rest were not?
• Does vCenter have some kind of built-in exception or logic that prioritizes system services (like VCSA) for auto-migration even when DRS is off?
• Is there a way to ensure all VMs migrate automatically when placing a host into maintenance, without enabling full DRS?

Any clarification or guidance from the community would be highly appreciated!

Thanks in advance,

Mohieldin

[Andrea Consalvi]

This is actually expected behavior even when DRS is disabled, vCenter will still try to protect itself.

When you place a host in maintenance mode without DRS, vMotion won't automatically migrate regular VMs, but vCenter-related system VMs (like the VCSA itself) will be moved automatically to ensure vCenter stays available. It's part of the built-in protection logic in vCenter it doesn't require DRS or HA.

So to answer your questions:

• Why did only the VCSA-related VMs migrate?
  Because vCenter has internal logic that prioritizes its own availability, especially for appliances running critical services (like vCenter or PSC nodes).

• Is there a way to migrate all VMs automatically without enabling DRS?
  Not automatically. Without DRS, full automation isn't available. You can script it using PowerCLI or use a custom vSphere Alarm → Trigger → Action mechanism, but out of the box, vMotion has to be done manually (except for those system VMs).

[Mohieldin Salam]

Thank you for the clarification regarding the VM migration behavior.

Your explanation makes perfect sense, I now understand that the automatic migration of the VCSA-related VMs during Maintenance Mode is expected, even without DRS enabled. It's helpful to know that vCenter has built-in logic to protect its own availability independently of DRS or HA configurations.

I also appreciate you confirming that without DRS, regular VMs won't migrate automatically and must be moved manually unless alternative automation (like scripting or alarms) is implemented.

[Andrea Consalvi]

I'm really glad the explanation was helpful, Mohieldin. Always happy to contribute!