The present disclosure relates generally to system migration, and in particular to migrating contents of a memory on a virtual machine.
System migrations of virtual machines are performed for a variety of reasons, including the ability to provide a back-up system while hardware and/or software upgrades are being installed. The virtual machine (including memory, system, applications, etc.) that is being copied is typically referred to as the source virtual machine and the virtual machine that is built as a result of the migration is referred to as the target virtual machine. One method of ensuring that the target virtual machine correctly reflects the contents of the source virtual machine is to halt execution of the source virtual machine to perform the migration. A snapshot is taken of the source virtual machine. The snapshot is utilized to create the target virtual machine and the target virtual machine is started. One problem with this approach is the system outage that occurs between the time that the source virtual machine is halted and the target virtual machine is started. Given that modern memories often include gigabytes and even terabytes of data, the system outage required to migrate the memory may be excessive.
Another approach to performing system migrations of virtual machines is to perform the migration while the source virtual machine is executing. This avoids the lengthy outage time to transfer the memory contents from the source memory to the target machine. However, this introduces a new problem of how to propagate updates (into memory on the target virtual machine) that occur to the memory on the source virtual machine while the migration is in process.
It would be desirable to be able to perform data migration in a manner that provides virtually uninterrupted service to the system users. This would require the ability to efficiently incorporate updates (into memory on the target machine) that occur to the memory on the source virtual machine while the migration is in process. Further, it would be desirable to be able transmit the data in an order that would likely result in fewer updates to the data after it has been migrated to the target virtual machine.