Methods for migrating data in a server that remains substantially available for use during such migration

摘要

Methods and software are provided for “hot migration” of data an original storage unit for a target system to destination storage unit. In one embodiment, a virtual storage device is provided, having a control block mapped to both the original storage unit, as well as to the destination storage unit. The target system is stopped, the virtual storage device is substituted for the original storage unit, and the target system is restarted. The virtual storage device directs requests to the destination storage unit, and fulfills read requests from whichever of the two storage units has a valid copy of data requested (depending, e.g., on whether the data is as yet unchanged, has been re-written, or has been copied, during the migration process). Unchanged data blocks are copies from the original storage unit to the destination storage unit. The target system is stopped, the virtual storage device is disconnected from the target system, and the destination storage unit is connected in its place. Software may also be provided to automate these processes.