Live guest migration
In a live guest migration, the system programmer relocates a KVM virtual server with a running Linux® instance from one KVM host to another without significantly disrupting operations.
Live guest migrations can help, for example, to avoid downtime during maintenance activities. A live guest migration can succeed only if both KVM hosts have access to equivalent resources. The hosts can but need not run on the same mainframe. The system programmer, who also initiates the migration, ensures that all preconditions are met.
If live migration is used at your installation, be sure not to block the migration. In particular:
- The virtual server configuration must not include any vfio_ap devices, which provide access to AP queues on cryptographic adapters.
- CCW and PCI pass-through devices must be detached before live migration.
- All tape device nodes must be closed and online tape drives must be unloaded.
- Any virtio-fs file systems, which are shared with the KVM host, must be unmounted.
- No program must be in a prolonged uninterruptible sleep state. Programs can assume this state while waiting for an outstanding I/O request to complete. Most I/O requests complete fast and do not compromise live guest migration. An example of an I/O request that can take too long to complete is rewinding a tape.