EM4J and DRS or vMotion

VMware Distributed Resource Scheduler (DRS) and VMware vMotion can migrate VMs from one host to another. When you migrate a VM with EM4J enabled, the result depends on whether the host to which the VM is migrated supports EM4J.

EM4J ballooning works with ESXi 5.0 and higher, but an EM4J-enabled VM can migrate to earlier ESX releases. This allows you to use EM4J-enabled VMs in an environment with mixed host versions, where it may be necessary to migrate a VM to an ESX or ESXi 4.1 host.


To move a VM from ESXi 5 to ESXi 4, the VM must be created as a Version 7 Virtual Machine. Version 8 is the default for ESXi 5.0.

If a VM is moved to another EM4J-compatible host while an EM4J-enabled JVM is running, EM4J will decouple the ballooned memory from the ESXi host and may create a new balloon on the new host, depending on the memory pressure the new host is experiencing. The ballooned memory will momentarily drop to zero when the VM is moved and will quickly achieve the new size required by the new host after migration.

If you move an EM4J-enabled VM to an ESX/ESXi 4.1 host, the VMware tools balloon is enabled if the host requires it. If the VM later migrates back to an ESXi 5.0 host, the EM4J balloon is again enabled.