12.3. Limitations for migrating virtual machines
Before migrating virtual machines (VMs) in RHEL 9, ensure you are aware of the migration’s limitations.
-
Migrating VMs from or to a session connection of
libvirtis unreliable and therefore not recommended. VMs that use certain features and configurations will not work correctly if migrated, or the migration will fail. Such features include:
- Device passthrough
- SR-IOV device assignment
- Mediated devices, such as vGPUs
- A migration between hosts that use Non-Uniform Memory Access (NUMA) pinning works only if the hosts have similar topology. However, the performance on running workloads might be negatively affected by the migration.
The emulated CPUs, both on the source VM and the destination VM, must be identical, otherwise the migration might fail. Any differences between the VMs in the following CPU related areas can cause problems with the migration:
CPU model
- Migrating between an Intel 64 host and an AMD64 host is unsupported, even though they share the x86-64 instruction set.
- For steps to ensure that a VM will work correctly after migrating to a host with a different CPU model, see Verifying host CPU compatibility for virtual machine migration.
- Firmware settings
- Microcode version
- BIOS version
- BIOS settings
- QEMU version
- Kernel version
Live migrating a VM that uses more than 1 TB of memory may in some cases not work reliably. The stability of such a migration depends on the following:
- The current workload of the VM
- The network bandwidth that the host can use for migration
- The downtime that your deployment is able to support
For live migration scenarios that involve VMs with more than 1 TB of memory, customers should consult Red Hat.
