Data migration without interrupting host access

An apparatus, comprising:

• a first virtual storage device;
• an alternate virtual storage device, the first virtual storage device configured to fail over to the alternate virtual storage device upon a migration error, read error, or write error;
• and
• a migration device configured to migrate data from a source storage device to a target storage device;
• and
• wherein the migration device is configured to:
• send write access requests received by the first virtual storage device, for data not subject to a lock, to the source storage device and the target storage device;
• hold write access requests subject to a lock;
• and
• send the held write access requests to the source storage device and the target storage device upon release of the lock.

A computer-readable medium storing a software program for migrating data that, when executed by a processor, causes the processor to:

• create a first and second virtual storage devices;
• migrate the data from a source storage device to a target storage device using both the first and second virtual storage devices;
• receive write access requests for the data being migrated at a respective first and second virtual storage device from a host during migration of the data;
• send received write access requests for a portion of the data being migrated that is not subject to a lock to the source storage device and the target storage device;
• hold received write access requests for the portion of data subject to the lock;
• and
• send the held write access requests from the respective first and second virtual storage device to the source storage device and the target storage device upon release of the lock such that the held write access requests do not expire.