VMware, Inc.
Upgrading on-disk format without service interruption

Abstract:

A logical map represents fragments from separate versions of a data object. Migration of data from a first (old) version to the second (new) version happens gradually, where write operations go to the new version of the data object. The logical map initially points to the old data object, but is updated to point to the portions of the new data object as write operations are performed on the new data object. A background migration copies data from the old data object to the new data object.